Control of tachyarrhythmias associated with Wolff-Parkinson-White syndrome by amiodarone hydrochloride

Amiodarone hydrochloride proved to be highly effective in preventing and treating arrhythmias of the Wolff-Parkinson-White (WPW) syndrome in 11 patients with WPW conduction and recurrent tachyarrhythmias. Paroxysmal supraventricular tachycardia (six patients), atrial fibrillation (four patients) and atrial flutter (one patient) were the most significant arrhythmias. In most patients the arrhythmia was seriously disabling because of the extremely rapid ventricular rate, adverse hemodynamic consequences and frequent recurrence and long duration of the episodes. Other known antiarrhythmic agents were ineffective. In all 11 patients amiodarone, in doses of 300 to 600 mg daily, totally, easily and safety controlled the arrhythmias for periods of 2 to 8 months. The drug was fully effective after an average of 7 days of treatment. Tolerance to amiodarone was excellent. The occurrence of corneal microdeposits of the drug was the only Important undesirable effect, but subjective ocular disturbances were not noted. The microdeposits are reversible, and can be avoided by discontinuing the drug for 7 days every 1 to 2 months. Amiodarone apparently causes a significant prolongation of refractoriness in the normal (A-V node and His-Purkinje system) as well as in the anomalous pathway, thus creating favorable conditions for prevention and Interruption of any reentry mechanism requiring participation of both pathways.     

DNA ligation in relation to DNA strand breaks in phytohemagglutinin- stimulated blast cells from acute lymphoblastic and nonlymphoblastic leukemia

DNA ligase activity was determined in the WBCs from 306 cases of acute lymphoblastic leukemia (ALL) and acute nonlymphocytic leukemia (ANLL). In T-ALL cells this activity was either low or absent. DNA analysis by nucleoid, alkaline elution, and alkaline sucrose centrifugation after cells were embedded in agarose inserts has shown more DNA breaks in T- ALL than in ANLL blasts. Phytohemagglutinin stimulation of T-ALL blasts resulted in the apparent joining of the DNA breaks. Apparent identical results can be obtained by the incubation of DNA with exogenous DNA ligase. The authors suggest that this enzyme is a crucially regulated step of replication and subsequent proliferation in this type of leukemia.     

Excess heme in sickle erythrocyte inside-out membranes: possible role in thiol oxidation

It has been suggested that the development of sickle RBC membrane defects might be related to abnormal amounts of membrane-associated heme (a term we use in its generic sense to include hemoglobins, hemichromes, and free heme). Techniques previously used to measure membrane heme, however, would not distinguish between what is truly membrane-associated and what is merely trapped in RBC ghost preparations. Consequently, we have examined extensively washed inside- out membranes (IOM) prepared from normal and sickle RBC. Approximately 25% of the sickle ghost heme is lost upon conversion to IOM, but sickle IOM still have a significant excess (1.6 +/- 0.3 nmol heme/mg membrane protein compared with 0.7 +/- 0.2 nmol/mg for normal IOM, P less than .001). Amounts of ghost heme are only poorly predictive of amounts of IOM heme (r = .664). Preparation of IOM by using isotonic lysis with saponin yields virtually identical amounts of IOM heme. Small amounts of heme (less than 15%) can be displaced from IOM by using manipulations that elute spectrin, displace electrostatically bound proteins, or cleave the cytoplasmic portion of band 3. Treatment of IOM with dithiothreitol (DTT), however, displaces the most heme (35%), and this is almost reproduced (25% displacement) by the treatment of intact RBC with DTT before IOM preparation. Sequential treatment with all manipulations still leaves about 40% of the heme in sickle IOM, which indicates a compartment more intimately associated with the membrane. At least part of this is free heme without globin, as evidenced by abnormal binding of radiochloroquine to sickle IOM. Conversely, some IOM-associated globin is globin without heme because the measurement of globin per se markedly overpredicts amount of IOM heme. There is a strong correlation between RBC density and amounts of either ghost or IOM heme. Finally, the amount of membrane thiol oxidation (as measured by thiol-disulfide-exchange chromatography) does not correlate at all with ghost heme (r = .105), but it correlates well with IOM heme (r = .877, P less than .001). These data demonstrate that there are abnormal amounts of heme truly associated with sickle RBC membranes, and they are consistent with the hypothesis that this membrane-associated heme participates in the pathobiology of the sickle RBC membrane, particularly those aspects perhaps related to thiol oxidation.     

Frequent deletion of p16INK4a/MTS1 and p15INK4b/MTS2 in pediatric acute lymphoblastic leukemia

The tandemly linked p16INK4aMTS1 and p15INK4b/MTS2 genes on chromosome 9, band p21 encode proteins that function as specific inhibitors of the cyclin D-dependent kinases CDK4 and CDK6. This locus undergoes frequent bi-allelic deletion in human cancer cell lines, suggesting that the encoded proteins may function as tumor suppressors. However, more recent analysis of primary tumor samples has shown a much lower frequency of abnormalities affecting this region, raising doubt over the importance of these proteins in human malignancies. Hemizygous deletions and rearrangements of chromosome 9, band p21, are among the most frequent cytogenetic abnormalities detected in pediatric acute lymphoblastic leukemia (ALL), occurring in approximately 10% of cases. To determine if the p16INK4a/p15INK4b locus might be the target of these chromosomal lesions, we analyzed both genes in primary clinical samples from 43 pediatric ALL patients using interphase fluorescence in situ hybridization, Southern blot analysis, and the polymerase chain reaction. Deletions of p16INK4a/p15INK4b were identified in 18 of 20 cases with cytogenetically observed abnormalities of 9p and 5 of 23 with apparently normal chromosomes 9p, with the majority containing bi- allelic deletions (16 homozygous/7 hemizygous). Although most homozygous deletions involved both genes, Southern blot analysis showed an interstitial deletion in a single case that was confined to p16INK4a, suggesting that p15INK4b was not the critical target gene in this case. Sequence analysis of both p16INK4a and p15INK4b in all seven cases with hemizygous deletions failed to show mutations within the coding regions of the retained alleles. In this select group of patients, deletion of p16INK4a/p15INK4b was associated with T-cell phenotype, nonhyperdiploid karyotype (< 50 chromosomes), and poor event- free survival. These findings indicate that deletion of the p16INK4a/p15INK4b locus is one of the most common genetic abnormalities so far detected in pediatric ALL, and that loss of one or more of these cell cycle kinase inhibitors is important in leukemogenesis.     

Antibody ligation of CD9 modifies production of myeloid cells in long- term cultures

The KMC8.8 monoclonal antibody was made by immunizing rats with the BMS2 stromal cell clone, and was selected for further study because its ability to inhibit production of myeloid cells in Dexter cultures but not that of lymphoid cells in Whitlock-Witte cultures. The influence on myeloid progenitors might have been indirect, since the antibody did not prevent responsiveness to colony-stimulating factors in semisolid agar cultures. Furthermore, there was no inhibition, and some augmentation, of cell production when the antibody was added to established Dexter cultures. A cDNA clone that encoded the KMC8.8- recognized molecule was isolated by expression cloning and found to be identical in sequence to a previously published murine CD9 homologue. The antibody and cDNA clone were used to establish that CD9 is expressed by stromal cells, megakaryocytes, platelets, myeloid cells, and subpopulations of mature lymphocytes in mice. Treatment with the KMC8.8/CD9 antibody slightly augmented adhesion between myeloid cells and stromal cells, consistent with previous reports that this member of the tetraspan family of proteins can transmit proadhesive signals to human platelets and lymphoid cells. CD9 might participate in cell-cell interactions critical for correct orientation and movement of maturing myeloid cells in bone marrow.     

Enhanced production of B lymphocytes after castration

Castration has long been recognized to stimulate thymic growth and augment cellular immunity. We sought to determine whether castration affects B lymphopoiesis by analyzing the phenotype of bone marrow and spleen cells from animals postcastration. In this report, we show that the bone marrow cells from castrated male mice show a sustained, twofold to threefold increase in numbers of B220+/IgM- cells and of newly formed B220+/IgM+ B cells. Most of the expanded B220+/IgM- cell population consisted of small, HSAhi, CD43- cells characteristic of pre- B cells. The castrated animals also showed increased numbers of splenic B cells, primarily consisting of small IgM+, IgDlo, B220lo, HSAhi cells. Taken together, these results show that castration causes dramatic, long-lived enhancement of B lymphopoiesis in bone marrow and increased numbers of mature B cells in the periphery.     

Inhibition of murine erythroid colony formation in vitro by interferon gamma and correction by interferon receptor immunoadhesin

It has been previously reported that inhibition of human erythroid colony-forming units (CFU-E) in vitro by interleukin-1 (IL-1) is an indirect effect, occurring through the production of interferon gamma (IFN gamma). IFN gamma, in turn, inhibits CFU-E colony formation directly, and its inhibitory effect can be overcome by exposure to high concentrations of erythropoietin (EPO). To develop an in vitro animal model for investigating inhibition of erythropoiesis by IFN gamma, the effects of recombinant murine (rm) IFN gamma on highly purified CFU-E from the spleens of mice infected with the anemia strain of the Friend virus (FVA) were studied. rmIFN gamma inhibited CFU-E colony formation in a dose-dependent manner. This inhibition occurred with large (> or = 8 cell) colonies only; smaller colonies were not affected. The inhibitory effect was corrected to 72% of control by high EPO concentrations of 64 U/mL. Murine CFU-E were then cultured with rmIFN gamma in the presence of a soluble murine IFN gamma receptor fused to the hinge and Fc domains of the human IgG1 heavy chain (mIFN gamma R- IgG). Inhibition of CFU-E colony formation by rmIFN gamma (100 U/mL) was corrected by mIFN gamma R-IgG in a dose-dependent manner, with an approximate IC50 of 0.05 nmol/L, and complete or near complete correction at 0.5 nmol/L. Similarly, a human IFN gamma R-IgG greatly reduced the inhibitory effect of recombinant human IFN gamma on human CFU-E. These experiments provide an in vitro animal model for studying the inhibitory effects of IFN gamma on erythropoiesis and indicate that IFN gamma R-IgG may be a useful agent for reducing the toxicity of IFN gamma in vivo.