Developmental regulation of cAMP signaling pathways in thymocyte development

Major developmental transitions in thymocyte differentiation are accompanied by sharp alterations in cAMP metabolism. We have analyzed the cAMP accumulation responses of cell populations representing successive stages of T-cell development, namely: immature TcR- thymocytes from SCID mice, proliferating cortical blasts, small cortical thymocytes, medullary thymocytes and peripheral T cells. We find that all classes of thymocytes exhibit higher cAMP synthesis in response to forskolin than peripheral T cells. In immature TcR- thymocytes, this high capacity is buffered by efficient phosphodiesterase activity, but in CD4+CD8+TcRlow thymocytes, phosphodiesterase activity becomes much less effective. Phosphodiesterase activity then rises again after positive selection. The ability of thymocytes to respond to prostaglandin E is regulated distinctly from their ability to respond to forskolin. Unlike forskolin, PGE1 induces cAMP synthesis to similar levels in all classes of thymocytes, possibly due to partial activation of phosphodiesterase in cortical thymocytes by PGE1. Finally, we report a novel effect of Ca2+/protein kinase C signaling on cAMP accumulation, which occurs selectively in the proliferating cortical blasts.     

The effects of high salt concentrations on the regulation of the substrate specificity of human recombinant deoxycytidine kinase

Deoxycytidine kinase (dCK) is a salvage pathway enzyme with broad substrate specificity that can phosphorylate both pyrimidine and purine deoxynucleosides, including important antiviral and cytostatic agents. The kinetic behaviour of dCK is complex with saturation curves showing negative cooperativity. In this study, we have expressed and affinity purified recombinant dCK, using the pET 9d vector system with a histidine tag-sequence and a thrombin cleavage site fused to the N-terminus of the dCK coding sequence. The His-tagged protein showed essentially the same kinetic properties as the protease cleaved protein and the purified protein isolated from human spleen. However, addition of 0.2-0.4 M NaCl during the dCK reaction caused a stimulation of 2'-deoxycytidine (dCyd), and the antileukemic analog 2-chlorodeoxyadenosine (CldAdo) phosphorylation, but an inhibition of the 2'-deoxyguanosine (dGuo) phosphorylation, both with His-tagged and protease cleaved dCK. The negative cooperativity observed with dCyd was eliminated by the presence of 0.4 M NaCl so that the Hill coefficient changed from 0.6 to 1.4. In contrast, dGuo phosphorylation that initially followed Michaelis-Menten kinetics showed negative cooperativity after addition of 0.4 NaCl. The alterations in kinetic properties were not accompanied by any apparent changes in subunit structure as revealed by gel filtration. The major form of dCK eluted in the position corresponding to a dimer in the presence or absence of salt, but a minor fraction of dCK, eluting in the position of a tetramer, was diminished in the presence of salt. The mechanism for the effects of 0.4 M NaCl on dCK kinetic behaviour is not known but it is most likely due to alterations in the conformation of the active site of the enzyme. The effects described here also may explain some of the discrepancies reported in the literature on the substrate specificity of this complex enzyme.     

Structure of the O-specific polysaccharide of Citrobacter freundii O3a,3b,1c

The following structure of the O-specific polysaccharide of Citrobacter freundii O3a,3b,1c containing D-mannose and D-rhamnose was established using sugar analysis and NMR spectroscopy, including computer-assisted analysis of the 13C NMR spectrum, 2D COSY, H,H-relayed COSY, heteronuclear 13C, 1H correlation (HETCOR), and rotating-frame NOE spectroscopy (ROESY):-->4)-alpha-D-Manp-(1-->3)-beta-D-Rhap-(1-->4) -beta-D-Rhap-(1-->.     

The use of Cordanum in combination with Corinfar-Retard for the treatment of ectopic arrhythmias in the sick sinus syndrome in patients with ischemic heart disease

38 patients with ischemic heart disease (IHD) and sick sinus syndrome (SSS) received combined therapy with nifedipine (Corinfar-Retard) and talinolol (Cordanum). The former drug had a positive chronotropic effect on the heart, the latter's chronotropic effect was slightly negative. All the patients had sinus bradycardia and ectopic arrhythmia which needed therapeutic correction: supraventricular and ventricular extrasystoles, fibrillation paroxysms or/and atrial flutter, paroxysmal supraventricular tachycardia, ventricular tachycardia. Cordanum was given in a dose 50 mg twice a day, Corinfar-Retard 20 mg twice a day for 16 days. 30 patients responded to the treatment. In addition to good subjective response, episodes of extrasystoles, paroxysms, flutter and fibrillation occurred much less frequently. Side effects resulted in the treatment discontinuation in 3 patients.     

Cyclic AMP-dependent anion secretion in human small and large intestine

Cyclic AMP-dependent Cl- secretion is the major secretion pathway in human intestine. The aim of the present study was to examine mechanisms involved in cAMP-dependent anion secretion in human small and large intestine. Surgical resection specimens from both jejunum and distal colon were studied under short circuited conditions. Addition of the phosphodiesterase inhibitor IBMX induced an increase in the short-circuit current (Isc) equivalent to the net increase in Cl- secretion. The Isc was inhibited by diphenylamine decarboxylate (DPC; Cl- channel blocker), bumetanide (basolateral Na+/K+/2Cl- cotransporter), BaCl2 (basolateral K+ channel) and Cl- free buffer in both segments and indomethacin (cyclo-oxygenase inhibitor) in colon alone. Diphenylamine decarboxylate appears to directly inhibit secretion in jejunum, although its inhibitory effect is possibly mediated by inhibition of cyclo-oxygenase in the colon. A small component of IBMX-stimulated Isc was inhibited by acetazolamide. Cyclic AMP-dependent secretion is largely apical Cl- secretion, although a small component appears to be HCO3. Secretion is dependent on basolateral K+ channels and Na+/K+/2Cl- cotransporters and, in the colon, is inhibited by indomethacin, implying a role for cyclo-oxygenase metabolites. The chloride channel blocker DPC inhibits secretion in both areas. This class of compounds may have potential for treatment of secretory diarrhoea.     

Parameters of estrogen expression in patients with endometrial tumors as prognostic signs of the effectiveness of neoadjuvant antitumor hormone therapy

Comparison was made of changes in such morphological characteristics of tumor as cell differentiation and mitotic activity in 142 patients with endometrial carcinoma in the course of treatment, using tamoxifen or oxyprogesterone capronate or both, and those of estrogen background (karyopicnotic, eosinophilic and maturity indices, numerical index of maturity and blood-estradiol level). Three levels of estrogen background-low, medium and high-were identified by assay of the colpocytological indices in postmenopausal patients with endometrial carcinoma. Levels of the colpocytological indices observed at high indices of estrogen background proved a reliable numerical criterion for evaluating the sensitivity of the patients to neoadjuvant hormone therapy. A significant correlation was established between high estrogen background, pathogenetic variant I and high differentiation of tumor cells. The high incidence of hormonal pathology in tumor tissue was registered when the colpocytological indices dropped by half after oxyprogesterone capronate treatment, and by third-after combined therapy (tamoxifen + oxyprogesterone capronate). In cases free from pronounced pathomorphism, said indices dropped by not more than 20%.     

Etiological role of cadmium in hypertension in an animal model

Dahl hypertension-resistant (R) and hypertension-sensitive (S) lines of rats were used to determine whether cadmium plays an etiological role in hypertension. In Study I, weanling (3-week-old) R and S rats of both sexes were given a low-salt (0.4% NaCl) diet and were divided into two groups. Rats in the cadmium group were injected with cadmium (2 mg/kg body weight, ip), whereas the controls received identical volumes of saline. Three weeks after the first injection, no elevations of systolic blood pressure were detected. A second dose of cadmium (1 mg/kg) produced hypertension in S females but not in S males or in R rats of either sex. Also, female S cadmium rats manifested significant (p less than 0.01) mild to moderate renal vascular changes. The concentrations of cadmium in hepatic and renal tissues of S cadmium rats were significantly higher (p less than 0.001) than in R rats. In Study II, weanling (3-week-old) female S rats on a high-salt (4% NaCl) diet were given cadmium (2 mg/kg body weight, ip) at week 3 followed by second and third injections of cadmium (1 mg/kg) at weeks 6 and 23. S controls received the same volumes of saline. Cadmium enhanced the rate and the degree of salt-induced hypertension development. Pathological lesions of periarteritis nodosa in the mesenteric arteries and renal vascular lesions occurred to the same extent in the cadmium and control groups. These data indicate that differences in genetic background influence the development of cadmium-induced hypertension in weanling rats, and that cadmium exacerbates the severity of salt-induced hypertension.     

Recognition of three epitopic regions on invasion plasmid antigen C by immune sera of rhesus monkeys infected with Shigella flexneri 2a

The invasive ability of Shigella spp. is correlated with the expression of several plasmid-encoded proteins, including invasion plasmid antigen C (IpaC). By characterizing the antigenic structure of IpaC with monoclonal antibodies and convalescent-phase sera, it may be possible to determine the physical location of specific epitopes as well as the involvement of epitopes in a protective immune response or the host's susceptibility to disease. By using overlapping octameric synthetic peptides, which together represent the entire IpaC protein, the precise linear sequence of four surface-exposed epitopes was defined for four IpaC monoclonal antibodies. Furthermore, 17 unique peptide epitopes of IpaC were mapped by using 9-day-postinfection serum samples from 13 rhesus monkeys challenged with Shigella flexneri 2a. Each individual recognized a somewhat different array of IpaC peptide epitopes after infection with shigellae. However, the epitopes were clustered within three regions of the protein: region I (between amino acid residues 1 and 61), region II (between amino acid residues 177 and 258), and region III (between amino acid residues 298 and 307). Region II was recognized by 92% of S. flexneri-infected individuals and was considered to be a highly immunogenic region. Animals asymptomatic for shigellosis after challenge with S. flexneri recognized peptide epitopes within all three epitopic regions of IpaC, whereas symptomatic animals recognized peptides in only one or two of the epitopic regions. Antibody from monkeys challenged with S. sonnei recognized IpaC peptide epitopes which fell within and outside the three S. flexneri epitopic regions. While numerous potential epitopes exist on the IpaC protein, the identification of three regions in which epitopes are clustered suggests that these regions are significant with respect to the immune response and to subsequent pathogenesis postinfection.     

The comparative study of peroxidase activity and substrate binding properties of cytochrome P450 2B4 incorporated into phospholipid vesicles with the use of two different methods

The comparative study of peroxidase activities and substrate binding properties of cytochrome p450 2B4 in reconstituted vesicles prepared with the use of two different techniques, and microsomal cytochrome P450 was carried out. The data obtained show that the two types of cytochrome P450 2B4-containing proteoliposomes do not differ substantially from each other with respect to H2O2- or cumene hydroperoxide-dependent substrate hydroxylation activities as well as substrate binding properties of hemoprotein reconstituted. However, some parameters measured with proteoliposomal cytochrome P450 are markedly different from those measured with microsomal hemoprotein, suggesting the existence of conformational differences between the molecules of these two cytochromes or the differences in the depth of their immersion into lipid bilayer.