Multiple possible sites of BRCA2 interacting with DNA repair protein RAD51

To investigate the biological consequences of aberrant BRCA2 protein during mammary carcinogenesis, we attempted to identify proteins that normally interact with BRCA2. By using a yeast two-hybrid system with a hybrid protein that contained residues 639-1,508 of BRCA2 protein fused to the GAL4 DNA-binding domain, we isolated five independent cDNA clones that encoded parts of RAD51 protein, a human homolog of bacterial RecA. In vitro experiments using anti-RAD51 antibody confirmed interaction of BRCA2 with RAD51. The RAD51-binding region of BRCA2 detected in the present study was distinct from the region reported recently. Further studies using smaller portions of BRCA2 defined at least two additional RAD51-binding domains, residues 982-1,066 and 1,139-1,266. Our results suggest that BRCA2 can interact with RAD51 through multiple sites of BRCA2 and that control of mitotic and meiotic recombination and/or of genomic integrity through binding to RAD51 may be a crucial mechanism by which BRCA2 suppresses abnormal proliferation of mammary cells.

Hypertrophic cardiomyopathy with apical left ventricular aneurysm

We report a case of hypertrophic cardiomyopathy (HCM) with apical left ventricular aneurysm, which is difficult to review because cases are so rare. A 54-year-old Japanese man was first found to have an electrocardiographic abnormality (T-wave inversion at rest) 19 years ago, and non-obstructive apical HCM without identifiable cause was diagnosed by echocardiography, left ventriculography, and clinical findings. After 19 years, he was admitted because of repeated episodes of palpitation and chest oppression at rest. Widespread left ventricular hypertrophy from the anteroseptal wall to the apex with an apical left ventricular aneurysm was detected by echocardiography, left ventriculography, and cardiac magnetic resonance imaging. Histologic examination of the hypertrophic apical myocardium surrounding the aneurysm showed that the myocardial tissue had been extensively replaced by fibrous tissue containing hypertrophic myocardial fibers, and uptakes of [123I]-metaiodobenzyl guanidine (MIBG) and [123I-] beta-methyliodophenyl pentadecanoic acid (BMIPP) in single-photon emission photography images were reduced despite high myocardial perfusion. On the other hand, histologic examination of the hypertrophic anterior wall revealed myocardial hypertrophy with disorganization; myocardial perfusion and the uptakes of MIBG and BMIPP were preserved. Abnormalities of myocardial fatty acid metabolism and sympathetic neuron activity with preserved perfusion flow and histologic changes such as fibrosis in the apical wall are indicative of apical myocardial injury or ischemia (infarction) without coronary artery stenosis; apical aneurysm may have occurred in severe apical HCM with cavity obliteration up to the midventricular level.

Multiplex mutation screening of the BRCA1 gene in 1000 Japanese breast cancers

To detect BRCA1 mutations in Japanese breast cancer patients, we screened 1,000 unselected primary cancers for mutations in exon 11, which accounts for 61% of the entire BRCA1 coding sequence. Using a method based on multiplex single-strand conformational polymorphism (SSCP) analysis of multiple restriction fragments generated by restriction-enzyme digestion of amplified DNA, we identified eight mutations. All eight were germline mutations; four of them were non-sense mutations or small deletions resulting in premature stop codons, and the other four were missense mutations. The Japanese carriers of these mutant BRCA1 alleles had developed breast cancers at ages ranging from 45 to 62, five of them bilaterally.

SHP-1 is involved in neuronal differentiation of P19 embryonic carcinoma cells

Accumulating evidence suggests that tyrosine phosphorylation plays an important role in the development of the central nervous system and in the differentiation of neuronal cells. To identify protein tyrosine phosphatases (PTPs) that might regulate signaling events leading to neuronal cell differentiation, we cloned PTP genes from the murine P19 embryonic carcinoma cell line and examined the change of their expression during differentiation. P19 cells are known to be pluripotent and the aggregate formation and subsequent replating in the presence of retinoic acid (RA) induce growth arrest and neuronal differentiation. The results demonstrated that among several PTP genes expressed in P19 cells, a cytosolic Src homology region 2 domain-containing PTP, SHP-1, is expressed highly in undifferentiated P19 cells, but is reduced to an undetectable level at day 3 after replating in the presence of RA. Further, SHP-1 was tyrosine-phosphorylated and activated at day 1 after replating. When ectopic SHP-1 was constitutively expressed, P19 cells continued to proliferate and failed to differentiate upon stimulation with RA. Collectively, these results suggest that the regulated expression and activity of SHP-1 may be involved in the neuronal differentiation of P19 cells.

Immunohistochemical detection of bone morphogenetic protein-2 and transforming growth factor beta-1 in tracheopathia osteochondroplastica

Tracheopathia osteochondroplastica (TO) is an unusual condition characterized by cartilaginous or bony submucosal nodules in the tracheobronchial tree. Bone morphogenetic protein-2 (BMP-2) and transforming growth factor beta-1 (TGF-beta 1) are potent inducers for new bone formation. We studied the precise localization of BMP-2 and TGF-beta 1 in two autopsied cases of TO, using immunohistochemical methods. Positive BMP-2 immunoreactivity was detected in numerous mesenchymal cells and chondroblasts lining the nodules in the tracheal submucosa. BMP-2 was not found in mature lamellar bony nodules. TGF-beta 1 was not seen in mesenchymal cells, though it did appear in chondrocytes and osteocytes in the nodules. These results suggest that BMP-2 plays an important role in nodule formation and acts synergistically with TGF-beta 1 to promote the nodules inductive cascade in the tracheal submucosa.

Hemodynamic effects of warm bathing in a Hubbard tank and exercise loading in patients after myocardial infarction

Hemodynamic parameters were measured during bathing and exercise testing in 43 patients with myocardial infarction (mean age: 60.2 years) to investigate the predictive parameters to determine when patients could safely resume bathing. Patients took a fresh water bath at 42 degrees C in the supine position for 5 min in a Hubbard tank. Group A showed an elevation of pulmonary capillary wedge pressure (PCWP) during bathing of 10 mmHg or more (23 patients, mean age: 61.7 years) and group B showed an elevation of less than 10 mmHg (20 patients, mean age: 60.5 years). Continuous multistep exercise tests were performed with a bicycle ergometer in the supine position, and hemodynamic parameters were measured at up to 50 W for 3 min on the day before the warm bathing test. There were no significant differences in the changes of arterial pressure and heart rate between the two groups. The PCWP at 3 min with a load of 50 W was significantly higher in group A (26.9 +/- 9.0 mmHg) than in group B (16.7 +/- 9.1 mmHg, p < 0.01). The stroke index (SI) during exercise testing was significantly lower in group A than in group B. The difference in the stroke index from baseline values (delta SI) at 3 min with a load of 50 W was significantly lower in group A (3.5 +/- 5.5 ml/m2/beat) than in group B (10.6 +/- 7.0 ml/m2/beat, p < 0.01). Similarly, delta CI and delta oxygen pulse during testing were significantly lower in group A than in group B. The physical work capacity and ejection fraction of the left ventricle of group A were significantly lower than those of group B, whereas the left ventricular end-diastolic pressure was higher in group A than in group B. CI, delta CI, SI, delta SI, METs, oxygen pulse, and delta oxygen pulse were examined by regression analysis and multivariate analysis to predict a significant elevation of delta PCWP during bathing. delta SI (p = 0.0032), delta CI (p = 0.0094), delta SI + METs (p = 0.0051), delta CI + METs (p = 0.0061), delta CI + delta SI (p = 0.0084), and delta CI + delta SI + METs (p = 0.0093) showed the highest correlations with delta PCWP. These findings suggest that changes in delta CI, delta SI, and METs are good predictive parameters for determining when patients may safely resume bathing. We suggest that patients with myocardial infarction, reduced cardiac function and a physical work capacity of approximately 4.0 METs, delta SI: 5 ml/m2/beat and delta CI: 2.4 l/min/m2 resume bathing only after careful consideration.

Smad1 and smad5 act downstream of intracellular signalings of BMP-2 that inhibits myogenic differentiation and induces osteoblast differentiation in C2C12 myoblasts

Bone morphogenetic protein-2 (BMP-2) inhibits terminal differentiation of C2C12 myoblasts and converts them into osteoblast lineage cells (Katagiri, T., Yamaguchi, A., Komaki, M., Abe, E., Takahashi, N., Ikeda, T., Rosen, V., Wozney, J. M., Fujisawa-Sehara, A., and Suda T. (1994) J. Cell Biol. 127, 1755-1766). In the present study, we examined the possible involvement of Smad proteins, vertebrate homologues of Drosophila Mothers against decapentaplegic, in the BMP effects on the differentiation of C2C12 myoblasts. C2C12 cells expressed Smad1, Smad2, Smad4, and Smad5 mRNAs, and expression levels were not altered by treatment with BMP-2 or TGF-beta1. When Smads were transiently transfected into C2C12 cells, both Smad1 and Smad5 induced alkaline phosphatase (ALP) activity and decreased the activity of myogenin promoter/chloramphenicol acetyltransferase (myogenin-CAT) without BMP-2. When C-terminal-truncated Smad1 and Smad5 were transfected into constitutively active BMP receptor type IB (BMPR-IB)-expressing C2C12 cells, BMP signals were blocked, resulting in an increase in myogenin-CAT activity. On the other hand, Smad1 and Smad5 decreased myogenin-CAT activity but did not induce ALP activity in MyoD-transfected NIH3T3 fibroblasts. These results suggest that both Smad1 and Smad5 are involved in the intracellular BMP signals which inhibit myogenic differentiation and induce osteoblast differentiation in C2C12 cells, and that the conversion of the two differentiation pathways is regulated independently at a transcriptional level.

Constitutively active BMP type I receptors transduce BMP-2 signals without the ligand in C2C12 myoblasts

Bone morphogenetic protein-2 (BMP-2), a member of transforming growth factor-beta superfamily, inhibits the terminal differentiation of C2C12 myoblasts and changes their differentiation pathway into cells expressing osteoblast phenotypes such as alkaline phosphatase (ALP) activity and osteocalcin production (Katagiri et al., 1994, J. Cell Biol. 127, 1755-1766). Two type I receptors for BMP-2 (BMPR-IA and BMPR-IB) have been cloned, but the role of the respective receptors in signal transduction is not clear. In the present study, we examined the signal transduction of BMP-2 in C2C12 cells using constitutively activated mutant BMPR-IA and BMPR-IB. C2C12 cells expressed BMPR-IA and BMPR-II mRNAs, but not BMPR-IB mRNA at detectable levels in Northern blotting. When mutated BMPR-IA and BMPR-IB were transiently transfected into C2C12 cells, both BMPR-IA and BMPR-IB similarly induced ALP activity in the absence of BMP-2. We also established subclonal cell lines of C2C12 cells by stably transfecting mutated BMPR-IB. When the mutated BMPR-IB-transfected cells were cultured in medium with low serum (differentiation medium) without BMP-2, the cells differentiated into ALP-positive mononuclear cells and not into myosin heavy chain-positive myotubes. These mutated BMPR-IB-transfected cells expressed ALP activity and osteocalcin mRNA in a time-dependent manner, but neither muscle creatine kinase nor myogenin mRNAs. These results indicate that the mutated BMP-2 type I receptors can constitutively transduce BMP-2 signals in the absence of the ligand in C2C12 cells.

Suppression of autoimmune disease and of massive lymphadenopathy in MRL/Mp-lpr/lpr mice lacking tyrosine kinase Fyn (p59fyn)

MRL/Mp-lpr/lpr (MRL/lpr) mice suffer from a generalized autoimmune disease that includes autoantibody production and glomerulonephritis and develop massive lymphadenopathy characterized by an expanded population of CD4- CD8- B220+ T cells that is derived from autoreactive T cells in the periphery. Some of us previously reported that these atypical T cells overexpressed a gene for tyrosine kinase p59fyn (Fyn). To define the role of Fyn in the renal disease and lymphadenopathy in MRL/lpr mice, we have generated Fyn-deficient MRL/lpr mice whose fyn gene is replaced by the gene for beta-galactosidase. Fyn-deficient MRL/lpr mice developed markedly limited disease and lived more than twice as long as the conventional MRL/lpr mice. In the mutant mice, the production of IgG3 anti-DNA autoantibody was significantly (p < 0.005%) reduced, and glomerular deposits of IgG3 and C3 were remarkably diminished. Ag receptor-mediated proliferative responses of Fyn-deficient splenic T cells were markedly impaired. The mutant mice showed delayed accumulation of the atypical CD4- CD8- B220+ T cells that exhibited a significantly lower activity of ZAP-70 compared with those in the conventional MRL/lpr mice. These data demonstrated that Fyn is involved as a positive regulator in the disease of MRL/lpr mice. Fyn provides a signal for both the expansion of autoreactive T cells and the production of IgG3 anti-DNA autoantibody by B cells. Thus, manipulation of Fyn may improve systemic autoimmune disease in humans.

Suppression of autoimmune disease and of massive lymphadenopathy in MRL/Mp-lpr/lpr mice lacking tyrosine kinase Fyn (p59fyn)

MRL/Mp-lpr/lpr (MRL/lpr) mice suffer from a generalized autoimmune disease that includes autoantibody production and glomerulonephritis and develop massive lymphadenopathy characterized by an expanded population of CD4- CD8- B220+ T cells that is derived from autoreactive T cells in the periphery. Some of us previously reported that these atypical T cells overexpressed a gene for tyrosine kinase p59fyn (Fyn). To define the role of Fyn in the renal disease and lymphadenopathy in MRL/lpr mice, we have generated Fyn-deficient MRL/lpr mice whose fyn gene is replaced by the gene for beta-galactosidase. Fyn-deficient MRL/lpr mice developed markedly limited disease and lived more than twice as long as the conventional MRL/lpr mice. In the mutant mice, the production of IgG3 anti-DNA autoantibody was significantly (p &lt; 0.005%) reduced, and glomerular deposits of IgG3 and C3 were remarkably diminished. Ag receptor-mediated proliferative responses of Fyn-deficient splenic T cells were markedly impaired. The mutant mice showed delayed accumulation of the atypical CD4- CD8- B220+ T cells that exhibited a significantly lower activity of ZAP-70 compared with those in the conventional MRL/lpr mice. These data demonstrated that Fyn is involved as a positive regulator in the disease of MRL/lpr mice. Fyn provides a signal for both the expansion of autoreactive T cells and the production of IgG3 anti-DNA autoantibody by B cells. Thus, manipulation of Fyn may improve systemic autoimmune disease in humans.

A kinase domain-truncated type I receptor blocks bone morphogenetic protein-2-induced signal transduction in C2C12 myoblasts

Members of the transforming growth factor (TGF)-beta superfamily bind the transmembrane serine/threonine kinase complex consisting of type I and type II receptors. Their intracellular signals are propagated via respective type I receptors. Bone morphogenetic protein (BMP)-2, a member of the TGF-beta superfamily, induces ectopic bone formation when implanted into muscular tissues. Two type I receptors (BMPR-IA and BMPR-IB) have been identified for BMP-2. We have reported that BMP-2 inhibits the terminal differentiation of C2C12 myoblasts and converts their differentiation pathway into that of osteoblast lineage cells (Katagiri, T., Yamaguchi, A., Komaki, M., Abe, E., Takahashi, N., Ikeda, T., Rosen, V., Wozney, J. M., Fujisawa-Sehara, A. and Suda, T. (1994) J. Cell Biol. 127, 1755-1766). In the present study, we examined the involvement of functional BMP-2 type I receptors in signal transduction in C2C12 cells, which expressed mRNA for BMPR-IA, but not for BMPR-IB in Northern blotting. TGF-beta type I receptor (TbetaR-I) mRNA was also expressed in C2C12 cells. Subclonal cell lines of C2C12 that stably expressed a kinase domain-truncated BMPR-IA (DeltaBMPR-IA) differentiated into myosin heavy chain-expressing myotubes but not into alkaline phosphatase (ALP)-positive cells, even in the presence of BMP-2. In contrast, the differentiation of the DeltaBMPR-IA-transfected C2C12 cells into myotubes was suppressed by TGF-beta1, as in the parental C2C12 cells. BMP-2 did not efficiently suppress the mRNA expression of muscle-specific genes such as muscle creatine kinase, MyoD, and myogenin, nor did it induce the expression of ALP mRNA in the DeltaBMPR-IA-transfected C2C12 cells. In contrast, TGF-beta1 inhibited mRNA expression of the muscle-specific genes in those cells. When wild-type BMPR-IA was transiently transfected into the DeltaBMPR-IA-transfected C2C12 cells, a number of ALP-positive cells appeared in the presence of BMP-2. Transfection of wild-type BMPR-IB or TbetaR-I failed to increase the number of ALP-positive cells. These results suggest that the BMP-2-induced signals, which inhibit myogenic differentiation and induce osteoblast differentiation, are transduced via BMPR-IA in C2C12 myoblasts.

Infrequent mutation of the H-cadherin gene on chromosome 16q24 in human breast cancers

To investigate the molecular basis of altered expression of the H-cadherin gene, we used polymerase chain reaction-single strand conformation polymorphism and DNA sequencing to examine the H-cadherin gene in 48 primary breast cancers in which loss of the long arm of chromosome 16 had been detected. We identified no mutations other than somatic 5-bp deletion within the coding region in a single tumor. The very low frequency of mutation found in these experiments suggests that H-cadherin is usually not a primary target for carcinogenesis in human breast cancers, and that reduction of its expression is likely to be a consequence of some other genetic event(s).

Changes in microsomal membrane phospholipids and fatty acids and in activities of membrane-bound enzyme in diabetic rat heart

Diabetes mellitus is associated with alterations in lipid metabolism and cardiac dysfunction despite an absence of coronary arteriosclerotic changes. To investigate mechanisms of cardiac dysfunction in diabetic cardiomyopathy, we studied the relation between activities of membrane-bound enzymes and surrounding phospholipids in rats with diabetes induced with a single intravenous injection of streptozotocin (65 mg/kg). We found that total phospholipid content of sarcoplasmic reticulum membrane increased significantly 8 weeks after treatment with streptozotocin owing to increases in phosphatidylcholine and phosphatidylethanolamine, a decrease in arachidonic acid, and an increase in docosahexaenoic acid in the early stage of diabetes. Sarcolemmal Na+/K(+)-ATPase activity and the number of receptors decreased in isolated cardiomyocytes of diabetic rats 8 weeks after streptozotocin administration. The Ca2+ uptake of both sarcoplasmic reticulum and mitochondria decreased simultaneously in permeabilized, isolated cardiomyocytes from diabetic rats. The depression of membrane-bound enzyme activities was correlated with alterations in phospholipids, which are closely related to the microenvironment of membrane-bound enzymes and influence intracellular Ca2+ metabolism. Because these changes in phospholipids and fatty acids were reversible with insulin therapy, they are diabetes-specific and might be a cause of cardiac dysfunction in diabetes.

Correlations between resting regional wall motion and regional myocardial blood flow (at rest and during exercise) in infarct-related myocardium--a study with [13N]ammonia positron emission tomography

We evaluated quantitatively the correlations between resting wall motion and regional myocardial blood flow (RMBF; at rest and during exercise) in infarct-related myocardium. The study was performed in 28 subjects: 21 patients who had previously suffered myocardial infarction of the anteroseptal wall, and 7 normal individuals. Positron emission tomography (PET) with [13N]ammonia was performed at rest and during low-grade exercise (bicycle ergometer fixed at 25 W for 6.5 min), and RMBF was measured quantitatively from the radioactivity in myocardial tissue and arterial blood. Resting regional wall motion was calculated using the centerline method on left ventriculographic findings. Resting regional wall motion was correlated with RMBF both at rest and during exercise in the infarct areas (anterior walls; y = 2.74 +/- 4.25 x 10(-2)x, r = 0.43, at rest; and y = -2.48 + 3.04 x 10(-2)x, r = 0.48, during exercise, p < 0.05; septal walls; y = -3.61 + 5.64 x 10(-2)x, r = 0.62, at rest; and y = -3.46 + 4.31 x 10(-2)x, r = 0.62, during exercise, p < 0.01). In each infarct-related wall, the coefficient (the slope) during exercise was smaller than that at rest (3.04 vs 4.25 and 4.31 vs 5.64 in each), and the infarct areas with preserved wall motion showed higher RMBF during exercise than those with reduced wall motion. Our results may show that wall motion depends on viable but ischemic myocardium in infarct-related walls.

Reversal of early metabolic dysfunction in hypertensive rat left-ventricular myocytes by angiotensin-converting enzyme inhibition

We evaluated the effects of angiotensin-converting enzyme (ACE) inhibition on metabolic changes in myocardial organelles, myocardial hypertrophy, and interstitial fibrosis in the early stage of hypertension. An ACE inhibitor, imidapril (2.5 mg/kg per day), a calcium-channel blocker, diltiazem (30 mg/kg per day), or vehicle was given to spontaneously hypertensive rats (SHRs) from 10 to 18 weeks of age. Single myocytes were isolated enzymatically from the left ventricles of these SHRs and normotensive Wistar-Kyoto (WKY) controls at 18 weeks of age. In single ventricular myocytes, enzyme activities in the sarcoplasmic reticulum (SR) and the sarcolemma (SL) and the mitochondrial respiratory control ratio (RCR) were determined. In 18-week-old SHRs receiving vehicle, myocardial hypertrophy and interstitial fibrosis developed, and SR Ca2+ AT-Pase activity and the mitochondrial RCR were significantly lower and SL Na+, K(+)-ATPase activity was significantly higher than in age-matched WKYs. However, compared with diltiazem, imidapril was better able to prevent the development of myocardial hypertrophy and interstitial fibrosis, to improve SR Ca(2+)-ATPase activity and the mitochondrial RCR, and to increase SL Na+, K(+)-ATPase activity. These results suggest that ACE inhibition can prevent the development of morphologic changes associated with hypertension-induced left ventricular remodeling, such as myocardial hypertrophy and interstitial fibrosis, and can counteract ongoing dysfunction of organelle metabolism early in the development of hypertension.

The effects of dopamine, dobutamine and amrinone on mitochondrial function in cardiogenic shock

The impairment of mitochondrial in non-infarcted myocardium under cardiogenic shock complicated by acute myocardial infarction was studied. We induced acute myocardial infarction in dogs by ligating the circumflex branch of the left coronary artery (LCX). On basis of left ventricular systolic pressure (LVPs) after 60 minutes, we divided the dogs into two groups: a group in which LVPs fell to below 70% of the pre-LCX ligation level, and a Control group in which LVPs remained more than 90%. The former group was further divided into four subgroups, depending on infusion of dopamine, dobutamine, amrinone or saline after 90 minutes. Mitochondria were prepared and mitochondrial respiratory activity determined. In the Saline group, hemodynamics became reduced to less than 70% of the preligation level after 120 minutes, however, in the Dopamine and Dobutamine groups, hemodynamics became restored to the preligation level. In the Amrinone group, LVPs decreased slightly, while cardiac output, LV Max. dp/dt and myocardial blood flow increased. In the Saline group, mitochondria in the non-infarcted myocardium functioned at a lower level of activity than that of the Control group. However, in the Dopamine, Dobutamine, and Amrinone groups, the mitochondria functioned at a higher level. Electron microscopy revealed mitochondrial damage in the Saline group only. The results indicate that an energy production disorder in the non-infarcted myocardium may have pathogenetic implications in cardiogenic shock associated with acute myocardial infarction, while dopamine, dobutamine, and amrinone improve mitochondrial function, and ultimately improve cardiac function.

Vitamin K2 and its derivatives induce apoptosis in leukemia cells and enhance the effect of all-trans retinoic acid

Geranylgeraniol, a polyprenylalcohol composing the side chain of vitamin K2 (VK2), was previously reported to be a potent inducer of apoptosis in tumor cell lines (Ohzumi H et al, J Biochem 1995; 117: 11-13). We examined the apoptosis-inducing ability of VK2 (menaquinone 3 (MK3), MK4 and MK5) and its derivatives such as phytonadione (VK1), as well as polyprenylalcohols with side chains of various lengths including farnesol (C15-OH; FO), geranylgeraniol (C20-OH; GGO), and geranylfarnesol (C25-OH; GFO) toward leukemia cells in vitro. MK3, MK4, MK5 and GFO (at 10 microM) showed a potent apoptosis-inducing activity for all freshly isolated leukemia cells tested and for leukemia cell lines such as NB4, an acute promyelocytic leukemia (APL)-derived cell line and MDS92, a cell line derived from a patient with myelodysplastic syndrome, although there were some differences depending on the cells tested. In contrast, VK1 showed no effect on any of the leukemia cells. The combination of MK5 plus all-trans retinoic acid (ATRA) resulted in enhanced induction of apoptosis in both freshly isolated APL cells and NB4 cells as compared to each reagent alone. These data suggest the possibility of using VK2 and its derivatives for the treatment of myelogenous leukemias, including APL.

Effects of adenosine triphosphate on ventriculoatrial conduction--usefulness and problems in assessment of catheter ablation of accessory pathways

The effects of adenosine triphosphate (ATP) on ventriculoatrial (VA) conduction were examined before and after accessory pathway (AP) ablation, with emphasis on assessment of the complication of dual atrioventricular (AV) node pathway. By evaluating the differences in the response to ATP of APs and other pathways, we assessed the usefulness and problems of this method. Of 59 patients who underwent AP ablation, 31 showed pre-excitation and 28 had concealed APs. A dual AV node pathway was found in 9 patients (15.3%) before ablation. After ablation, a dual AV node pathway was newly found in 9 patients. Thus, the total number of patients with a dual AV node pathway was 18 (30.5%). VA conduction over APs was not blocked in 26 of 29 patients, but the remaining 3 APs were blocked transiently by ATP. ATP caused VA block over the AV node in 15 of 16 patients and a dual AV node pathway in all 11 patients. In contrast, VA conduction over the retrograde fast pathway was blocked in 9 of 14 patients with AV node re-entrant tachycardia. ATP has little effect on APs, so observation of the response to ATP provides a more reliable and useful means of evaluating successful ablation. With this method, however, it is important to consider the possibility of the presence of ATP-sensitive APs and ATP-resistant retrograde fast pathways. The influence of ablation-induced injury has not been fully clarified. It is therefore essential to take into account various data, including the comparison between data obtained before and after ablation.

Elevation of circulating proadrenomedullin-N terminal 20-peptide in thyrotoxicosis

BACKGROUND AND OBJECTIVE

Adrenomedullin (AM) is a recently discovered peptide which has potent vasodilatory activity. We have found that the plasma adrenomedullin level is elevated in hyperthyroidism, suggesting a potential role of AM in the decrease of vascular resistance in thyrotoxicosis. Proadrenomedullin, a precursor of adrenomedullin, yields another peptide termed proadrenomedullin-N terminal 20-peptide (PAMP). PAMP also has potent vasodilatory activity. Although the regulation of secretion of AM and PAMP is not fully understood and the mechanism by which the plasma AM level is elevated in hyperthyroidism remains unknown, it is of interest to determine the plasma concentration of PAMP in thyrotoxicosis.

DESIGN AND PATIENTS

We measured the plasma concentration of immunoreactive AM and PAMP in newly recruited untreated thyrotoxic Graves' patients using specific antibodies to each peptide.

RESULTS

Not only AM, but also the plasma concentration of PAMP in thyrotoxic patients was significantly (P < 0.01) elevated (4.7 +/- 0.9 pmol/l), compared to that in control subjects (2.6 +/- 0.8 pmol/l). The correlation was marginally significant between the plasma AM concentration and serum free thyroid hormone levels. The plasma PAMP level tended to be more elevated when thyrotoxicosis was severe but the correlation was not statistically significant. Correlation was not demonstrated between the AM and PAMP levels in thyrotoxic patients.

CONCLUSIONS

Elevation of the plasma adrenomedullin and proadrenomedullin-N terminal 20-peptide levels raises the possibility of involvement of these vasodilatory peptides in the haemodynamic changes in thyrotoxicosis.

Significance of downsloping ST-segment depression induced by low-level exercise in severe coronary artery disease. Assessment with myocardial ischemia and collateral perfusion

Exercise-induced downsloping ST-segment depression is a common manifestation of severe myocardial ischemia. Although greater downsloping ST-segment depression is suspected to indicate more severe ischemia, its exact relationship to regional myocardial blood flow (RMBF) has not yet been clarified. We investigated the relationship between the magnitude of downsloping ST-segment depression and exercise-induced changes in RMBF and collateral perfusion. Nitrogen-13 ammonia positron emission tomography was performed in 6 healthy volunteers and 72 patients with angiographically proven coronary artery disease. The left ventricle was divided into 11 regions of interest, and RMBF in each region was measured at rest and during low-level supine bicycle exercise. Downsloping ST-segment depression of 0.1 mV or more at 80 milliseconds after the J point was accepted as significant. Low-level exercise induced downsloping depression of 0.1 to 0.2 mV in 10 patients (group D1) and downsloping depression of 0.2 mV or more in 8 patients (group D2). Multivessel disease was common in both group D1 (80% of patients) and group D2 (88% of patients). Collateral circulation was significantly more frequent in group D1 (90%) than in group D2 (13%, p < 0.01). Ischemic areas were larger and cardiac function was worse in group D2 than in group D1. The RMBF increased sufficiently in all regions (56 +/- 30%) with exercise in the healthy group. In group D1, RMBF was unchanged or decreased in ischemic areas (10 +/- 23%) but increased sufficiently in surrounding areas (50 +/- 32%). In group D2, RMBF was unchanged in ischemic areas (17 +/- 24%) and increased insufficiently in surrounding areas (41 +/- 21%). Therefore, exercise-induced downsloping ST-segment depression of 0.1 to 0.2 mV may reflect an underlying change in blood flow in viable myocardium with collateral perfusion, and downsloping depression of 0.2 mV or more may reflect more severely impaired myocardium without collateral perfusion.

Spontaneous lesions of nasal cavity in aging F344 rats and BDF1 mice

The outline of spontaneous lesions of the nasal cavity that were commonly observed in F344 rats and BDF1 mice used as untreated control groups in ten 2-year carcinogenicity studies were presented. In rats, the common spontaneous lesions were eosinophilic change of the respiratory epithelium and the olfactory epithelium, respiratory metaplasia of glands and the olfactory epithelium, foreign body inflammation, deposit of calcium, and thrombus. In mice, the common spontaneous lesions were eosinophilic change of the respiratory epithelium and olfactory epithelium, and respiratory metaplasia of glands and the olfactory epithelium. Some of these lesions revealed either species or sex-related differences of incidence.

Protective effect of captopril on ischemic myocardium

The protective effect and mechanism of action of the angiotensin-converting enzyme inhibitor (ACE-I) captopril was investigated in organelles from ischemic myocardial cells in a canine coronary ligation model. Sarcoplasmic reticulum (SR) and mitochondrial fractions were extracted from ischemic and nonischemic myocardial cells from captopril- and saline-treated (control) hearts. Heart rate, cardiac output, and right ventricular systolic blood pressure were similar in the captopril-treated and control groups. Left ventricular systolic blood pressure (LVPs) decreased gradually to 89% of the baseline value after captopril administration, and to 78% of the baseline value after ligation. Ca-ATPase activity in the SR, the respiratory control ratio (RCR) in the mitochondria, and dinitrophenol (DNP)-stimulated ATPase activity were significantly higher in ischemic myocardium from the captopril-treated group than from the saline-treated (control) group. The SH group content of both organelles was higher in the captopril-treated group. Our results suggest that, in addition to their hemodynamic effects, ACE-I agents containing SH groups protect the myocardium from ischemic damage by preventing enzyme oxidation.

Bone morphogenetic protein-2 inhibits terminal differentiation of myogenic cells by suppressing the transcriptional activity of MyoD and myogenin

Bone morphogenetic protein (BMP) is a family of cytokines that induce ectopic bone formation when implanted into muscular tissues. We reported that BMP-2 inhibits the terminal differentiation of C2C12 myoblasts and converts them into osteoblast lineage cells (Katagiri, T., Yamaguchi, A., Komaki, M., Abe, E., Takahashi, N., Ikeda, T., Rosen, V., Wozney, J. M., Fujisawa-Sehara, A., and Suda, T. (1994) J. Cell Biol. 127, 1755-1766). In the present study, we examined the molecular mechanism of the inhibitory effect of BMP-2 on terminal differentiation of myogenic cells. When either MyoD or myogenin cDNA was introduced into C3H10T1/2 (10T1/2) cells with a muscle-specific CAT reporter containing four copies of the right E-box of muscle creatine kinase (MCK) enhancer, the CAT activity was dose-dependently suppressed by BMP-2. Furthermore, BMP-2 inhibited the terminal differentiation of these subclonal 10T1/2 cells that stably expressed MyoD or myogenin into mature myotubes that expressed myosin heavy chain and troponin T. The differentiation of a subclone of the MyoD-transfected NIH3T3 cells into mature muscle cells was also inhibited by BMP-2. BMP-2 induced alkaline phosphatase activity in 10T1/2-derived, but not in NIH3T3-derived MyoD-transfected cells. These cells constitutively expressed exogenous MyoD and myogenin, which were localized exclusively in the nuclei irrespective of the presence and the absence of BMP-2. However, these cells failed to express the mRNAs of endogenous myogenic factors and MCK when cultured with BMP-2. In the electrophoresis mobility shift assay using nuclear extracts of the myogenic cells, MyoD and myogenin bound to the right E-box in the enhancer region of the MCK gene even in the presence of BMP-2. These results suggest that BMP-2 inhibits the terminal differentiation of myogenic cells by suppressing the transcriptional activity of the myogenic factors.

Isolation and mapping of karyopherin alpha 3 (KPNA3), a human gene that is highly homologous to genes encoding Xenopus importin, yeast SRP1 and human RCH1

From a human fetal-brain cDNA library, we isolated and characterized a novel gene (KPNA3) encoding a protein highly homologous to certain nuclear transport proteins of Xenopus and human. The complete cDNA clone, designated karyopherin alpha 3, contained an open reading frame of 1,563 nucleotides encoding 521 amino acids. The predicted amino acid sequence showed 48%, 45% and 48% identity with Xenopus importin, yeast SRP1 and human RCH1, respectively. The similarities among these proteins suggest that karyopherin alpha 3 may be involved in the nuclear transport system. Eight repeats of the arm motif were well conserved among these proteins. The N-terminal region of the predicted karyopherin alpha 3 product was highly basic and the C-terminal region was strongly acidic. A 4.3-kb transcript was expressed in all adult human tissues examined by Northern blotting. The cDNA clone was assigned to chromosome band 13q14.3 by fluorescence in situ hybridization.