Antimalarial properties of ebselen

The seleno-organic compound ebselen showed anti-malarial activity in vitro against the murine Plasmodium berghei and the human P. falciparum. In P. berghei, the uptake and incorporation of [3H]-methionine and [3H]-adenosine was inhibited and the infectivity of plasmodia was reduced. Ebselen affects the development of asexual stages of chloroquine-resistant and -sensitive P. falciparum strains. Its IC50 for P. falciparum was about 14 mumol/l and that for P. berghei, about 10 mumol/l. The growth of P. falciparum was blocked by ebselen at all stages, including the invasion of erythrocytes by merozoites. In a human hepatoma cell line and in mouse peritoneal macrophages, no cytostatic or cytotoxic effects were found, indicating selective inhibition of plasmodia by ebselen. Its in vitro inhibitory effect is discussed in relation to its possible reactivity with thiol groups and its lack of an anti-malarial effect in infected mice.

Determination of Settings of a Tilted Head Cutter for Generation of Hypoid and Spiral Bevel Gears

Kinematics of mechanisms of hypoid and spiral bevel cutting machines is considered. These mechanisms are designated to install the position and tilt of the head cutter. The tilt of the head cutter with standard blades provides the required pressure angle. The authors have developed the matrix presentation of kinematics of these mechanisms and basic equations for the required settings. An example is presented based on the developed computation procedure.

Mitochondria contain a proteolytic system which can recognize and degrade oxidatively-denatured proteins

When incubated with mitochondria in an air atmosphere, menadione and doxorubicin (which redox cycle with the respiratory chain to produce oxygen radicals), as well as xanthine oxidase plus xanthine (which generate superoxide and H2O2), stimulated the degradation of newly-synthesized [( 3H]leucine-labelled) mitochondrial polypeptides. No stimulation was observed in an N2 atmosphere, ATP was not required, and xanthine oxidase was not effective without xanthine. Various forms of oxidative stress induced varying degrees of protein cross-linking, protein fragmentation and proteolysis, as judged by gel electrophoresis and amino acid analysis. To learn more about the proteolytic enzymes involved in degradation, we undertook studies with purified protein substrates which had been exposed to oxidative stress (OH or H2O2) in vitro. Despite mitochondrial contamination with acid proteases of lysosomal (and other) origin, pH profiles revealed distinct proteolytic activities at both pH 4 and pH 8. The pH 8 activity preferentially degraded the oxidatively-denatured forms of haemoglobin, albumin and superoxide dismutase; was unaffected by digitonin; and exhibited a several-fold increase in activity upon mitochondrial disruption (highest activity being found in the matrix). In contrast, the pH 4 activity was dramatically decreased by digitonin treatment (to reduce lysosomal contamination); was unaffected by mitochondrial disruption; and showed no preference for oxidatively-denatured proteins. The pH 8 activity was not stimulated by ATP, but was inhibited by EDTA, haemin and phenylmethylsulphonyl fluoride. In contrast, the contaminating pH 4 activity was only inhibited by pepstatin and leupeptin. Thus, our experiments reveal a distinct mitochondrial (matrix) proteolytic pathway which can preferentially degrade oxidatively-denatured proteins.

Synthesis of interleukin 6 (interferon-beta 2/B cell stimulatory factor 2) in human fibroblasts is triggered by an increase in intracellular cyclic AMP

Interleukin 6 (IL-6; also referred to as interferon-beta 2, 26-kDa protein, and B cell stimulatory factor 2) is a cytokine whose actions include a stimulation of immunoglobulin synthesis, enhancement of B cell growth, and modulation of acute phase protein synthesis by hepatocytes. Synthesis of IL-6 is stimulated by interleukin 1 (IL-1), tumor necrosis factor (TNF), or platelet-derived growth factor. We examined the role of the cyclic AMP (cAMP)-dependent signal transduction pathway in IL-6 gene expression. Several activators of adenylate cyclase, including prostaglandin E1, forskolin, and cholera toxin, as well as the phosphodiesterase inhibitor isobutylmethylxanthine and the cAMP analog dibutyryl cAMP, shared the ability to cause a dramatic and sustained increase in IL-6 mRNA levels in human FS-4 fibroblasts. Actinomycin D treatment abolished this enhancement. Treatments that increased intracellular cAMP also stimulated the secretion of the IL-6 protein in a biologically active form. Increased intracellular cAMP appears to enhance IL-6 gene expression by a protein kinase C-independent mechanism because down-regulation of protein kinase C by a chronic exposure of cells to a high dose of 12-O-tetradecanoylphorbol 13-acetate did not abolish the enhancement of IL-6 expression by treatments that increase cAMP. IL-1 and TNF too increased IL-6 mRNA levels by a protein kinase C-independent mechanism. Our results suggest a role for the cAMP-dependent pathway(s) in IL-6 gene activation by TNF and IL-1.

T cell epitopes in experimental autoimmune myasthenia gravis of the rat: strain-specific epitopes and cross-reaction between two distinct segments of the alpha chain of the nicotinic acetylcholine receptor (Torpedo californica)

T cell epitopes on the nicotinic acetylcholine receptor (A ChR) of Torpedo californica were analyzed using T cell lines isolated from Lewis, BN, and (Lewis X BN)F1 rats. All lines selected for reactivity against either native or denatured AChR or for 6 selected synthetic peptides of the AChR alpha chain expressed the CD4 membrane phenotype and recognized their antigen in the context of major histocompatibility complex class II determinants. They were tested in vitro for reactivity with each of these antigens. The results indicate that parental Lewis and BN rat T lymphocytes recognize distinct molecular epitopes on the AChR protein, whereas (Lewis X BN)F1 hybrids respond against both sets of epitopes. Two peptides (P10 and P11) which represent distinct amino acid sequences on the putatively extracellular part of the AChR alpha chain, and which share only 4 common amino acids, two of them contiguous, showed an unexpected cross-reactivity in the Lewis rat. T cells selected for either peptide co-recognize the other peptide in vitro. In addition, these cells are responsive against full length AChR. P11, in particular, appears to be a major epitope for Lewis rats immunized with AChR.

Glutathione reductase-deficient erythrocytes as host cells of malarial parasites

BCNU [1,3-bis(2-chloroethyl)-1-nitrosourea] and its less toxic derivative HeCNU [1-(2-chloroethyl)-3-(2-hydroxyethyl)-1-nitrosourea] are clinically-used antitumour drugs. In erythrocytes BCNU is a highly specific inhibitor of the enzyme glutathione reductase [H. Frischer and T. Ahmad, J. Lab. clin. Med. 89, 1080 (1977)]. When treating erythrocytes in vitro, 50% enzyme inhibition was obtained with 1 microM BCNU or 3 microM HeCNU within 2 hr. The two drugs were used for preparing red cell populations with various levels of glutathione reductase activity; complete inhibition (greater than or equal to 98%) was only achieved when the medium contained glucose as a source of reducing equivalents. The erythrocytes were then tested in drug-free media as host cells for the malaria parasite Plasmodium falciparum. In the range of 0-300 mU/ml cells, there was a correlation between glutathione reductase activity and parasite growth; erythrocytes with an activity of less than 20 mU/ml did not serve as host cells for P. falciparum at all although these erythrocytes were viable. When the culture medium was supplemented with 20 mM glutathione (GSH), parasite growth was normal irrespective of the glutathione reductase level in the erythrocytes. This is consistent with the finding that poisoning glutathione reductase led to a 10-fold decrease of the cytosolic GSH level. Our results corroborate the concept that intraerythrocytic inhibition of glutathione reductase mimicks the biochemistry of drug-sensitive glucose-6-phosphate dehydrogenase deficiency (favism), an inherited condition which confers protection from malaria.

Site-directed mutagenesis of a residue located in the regulatory site of Escherichia coli aspartate transcarbamoylase. Involvement of lysine 94 in effector binding and the allosteric mechanism

Lysine 94 in the regulatory chain of aspartate transcarbamoylase has been changed to a glutamine residue by site-directed mutagenesis. The resulting enzyme is almost insensitive to the activator ATP and shows a substantially reduced response to the feedback inhibitor CTP. Competition experiments indicate that ATP is still able to bind at low concentrations to the regulatory site of the mutant enzyme, even though no stimulation could be detected. When the nucleosides adenosine or cytidine were used, the saturation curves of the mutant and the wild-type enzyme became indistinguishable. Together these results indicate that lysine 94 is strongly involved in the binding of ATP and CTP by interacting specifically with the triphosphate moiety of these nucleotide effectors. Furthermore, unlike the wild-type enzyme, the inhibitory and stimulatory effects in the mutant enzyme are insensitive to changes in aspartate concentrations, implying that the lysine 94 side chain is also involved in the allosteric mechanism of the enzyme.

X-ray Line Broadening Study on Shock-modified Zirconia

Zirconia (Zr02) powder compacts have been subjected to controlled, quantitative high pressure shock loading at peak pressures from 5-27 GPa and preserved for post-shock analysis. The overlapping broadened X-ray diffraction peak profiles have been separated by least-squares fitting procedures. The separate lines have been analysed in the usual manner to determine the residual lattice strain and the coherent crystallite sizes. Maximum modification effects are observed near 20 GPa with strain values near 3 x 10-3 and size values near 200 A.

Mapping of human fibronectin receptor beta subunit gene to chromosome 10

Human-mouse hybrid cells were examined by indirect immunofluorescence with Mab DH12, a monoclonal antibody that recognizes the beta subunit of the human fibronectin receptor. Cells that expressed the antigen at their surface were sorted by FACS and karyotyped. Immunoaffinity chromatography on Mab DH12 was used to confirm the presence of the human antigen. The chromosome assignment was strengthened by isozyme analysis of markers for chromosomes 9 and 10. The results are suggestive for a 10p mapping of this beta subunit of the fibronectin receptor. Since the gene coding for the beta subunit of the VLA proteins was previously assigned to the same chromosome, our result could provide further evidence for the relationship between the beta subunit of the human fibronectin receptor and the VLA protein family.

Inhibition of hemoglobin degradation in Plasmodium falciparum by chloroquine and ammonium chloride

The effect of chloroquine (CQ) and NH4Cl on hemoglobin degradation within Plasmodium falciparum was studied by SDS gel electrophoresis. CQ inhibited hemoglobin digestion such that accumulation of hemoglobin in the parasites occurred. Quantitative analysis indicated that the content of hemoglobin in isolated CQ-treated parasites was increased from 2.39 +/- 0.47 micrograms hemoglobin (Hb)/mg protein to 8.34 +/- 0.77 micrograms Hb/mg protein (P less than 0.001) within 45 min and further to 18.7 +/- 1.23 micrograms Hb/mg protein for 2 hr compared with the untreated parasites. These results suggest that the inhibition of hemoglobin degradation in malarial parasites might be the primary target of CQ antimalarial action. The CQ-like effect on the hemoglobin digestion in P. falciparum was observed with another lysosomotropic weak base, NH4Cl, suggesting that the CQ effect on hemoglobin degradation and its antimalarial action, as well as the effect of NH4Cl, are related to their properties of lysosomotropic weak base.

Electrolyte transport in a central core model of the renal medulla

Transport of Na+, K+, Cl-, urea, and water is described in a central core model of the renal medulla. Equations for mass balance, Poiseuille flow, and the Nernst-Planck equation describe the continuous behavior of the system along the medullary axis and along the distal nephron; the Kedem and Katchalsky phenomenology describes passive transmural transport; active transmural transport obeys Michaelis-Menten kinetics. Numerical solution of the differential equations shows that to a close approximation any combination of active Na+ and active Cl- transport can generate the same concentration profiles but will generate very different potential profiles, and consequently, very different K+ absorption in thick ascending limb of Henle's loop. If a net transport stoichiometry of 2 Cl- ions to 1 Na+ ion is selected for the pumps, an active Cl- transport rate of approximately 10,000 peq.s-1.cm-2 gives K+ and Na+ concentrations in early distal nephron and a medullary osmolality profile in reasonable agreement with experimental data.

Effects of some alcohols on the conformation of mitochondrial H+-ATPase complex and F1-ATPase from pig heart

The conformations of the H+-ATPase complex and F1-ATPase in low concentrations of methanol, ethanol, n-propanol, iso-propanol and t-butanol were studied by circular dichroism. For F1-ATPase, all but methanol first increased and then decreased the circular dichroism magnitude of helical bands as the alcohol concentration was increased. With ethanol, n-propanol, iso-propanol and t-butanol, the alpha-helix content reached a maximum at about 5% alcohol and began to decrease at 10%. The content of beta-sheet showed the opposite effect, reaching a minimum at 5% and increasing slightly at higher concentrations. None of the alcohols studied had a significant effect on the conformation of the H+-ATPase complex. This difference implies that the alcohols had a greater effect on free F1-ATPase than on the membrane-bound F1-ATPase. The hydrophobic protein F0 and the membrane lipids in the H+-ATPase complex may stabilize and protect F1 from the effects of the alcohols.