The muscarinic M1 agonist xanomeline increases soluble amyloid precursor protein release from Chinese hamster ovary-m1 cells

The functionally selective M1 agonist xanomeline, which is currently undergoing clinical trials as a therapy for Alzheimer's disease, was compared to the muscarinic agonist carbachol for effects on secretion of soluble amyloid precursor protein (APPs) from Chinese hamster ovary cells transfected with the human m1 receptor (CHO-m1). Release of APPs from CHO-m1 cells was increased maximally (4-10 fold) by 100 microM carbachol (EC50 = 11 microM) and by 100 nM xanomeline (EC50 = 10 nM). Stimulation of APPs secretion by xanomeline and carbachol was blocked by preincubation with 1 microM atropine. Carbachol did not stimulate APPs secretion from non-transfected CHO cells. Pilocarpine at 1 mM also increased APPs release. The efficacy of carbachol, xanomeline and pilocarpine for stimulating APPs secretion did not differ significantly. Activation of protein kinase C (PKC) in m1 transfected cell lines by 1 microM phorbol dibutyrate (PDBu) increased APPs release, and this was inhibited 97% by the PKC inhibitor bisindolemalemide. The PKC inhibitor decreased xanomeline and carbachol-stimulated APPs secretion by only 25-30%. These results demonstrate that xanomeline increased APPs release by activation of m1 muscarinic receptors and support the possibility that cholinergic replacement therapy for Alzheimer's Disease may reduce amyloid deposition.     

Misincorporation of dNTPs opposite 1,N2-ethenoguanine and 5,6,7,9-tetrahydro-7-hydroxy-9-oxoimidazo[1,2-a]purine in oligonucleotides by Escherichia coli polymerases I exo- and II exo-, T7 polymerase exo-, human immunodeficiency virus-1 reverse transcriptase, and rat polymerase beta

1,N2-Ethenoguanine (1,N2-epsilon-Gua) and 5,6,7,9-tetrahydro-7-hydroxy-9-oxoimidazo[1,2-a]purine (HO-ethanoGua) are two modified bases formed in the reaction of DNA with 2-chlorooxirane, the epoxide derivative of vinyl chloride. The oligonucleotides (19-mers), 5'-CAGTGGGTG*TCCGAATTGA-3', were prepared, with each of these modified bases substituted for G at G*. HO-ethanodeoxyguanosine exists predominantly as a mixture of diastereomers of the closed cyclic hemiaminal form, 5,6,7,9-tetrahydro-7-hydroxy-9-oxoimidazo[1,2-a]purine, shown by H2(18)O experiments to be in equilibrium with the open form, N2-(2-oxoethyl)Gua. Both adducts retarded the 3'-extension of a complementary 10-mer primer by all of the polymerases examined, but in every case, some full-length product was obtained. Nucleotide sequence analysis indicated misincorporation of dGTP and dATP across from both 1,N2-epsilon-Gua and HO-ethanoGua, with the extent varying considerably among the polymerases. Similar results were obtained when the abilities of the polymerases to incorporate a single dNTP were evaluated. In addition, -1 and -2 base frame shifts were detected with both 1,N2-epsilon-Gua and HO-ethanoGua with some of the polymerases. Steady-state kinetic experiments with Escherichia coli polymerase I exo- and T7 polymerase exo-/thioredoxin showed large decreases in k(cat) for all dNTP incorporations compared to the normal G x dCTP pair and high misincorporation frequencies for dATP and dGTP with both adducts (compared to dCTP). Collectively, the results indicate that both of these adducts have considerable miscoding potential with some of these polymerases, that there are a number of differences between the 1,N2-epsilon-Gua and HO-ethanoGua adducts (which formally differ only in the presence of the elements of water), and that misincorporation of dNTPs at a single modified base can vary considerably among different polymerases even in the absence of exonuclease activity.     

ABT-089 [2-methyl-3-(2-(S)-pyrrolidinylmethoxy)pyridine]: I. A potent and selective cholinergic channel modulator with neuroprotective properties

Lactate dehydrogenase from the malarial parasite Plasmodium falciparum has many amino acid residues that are unique compared to any other known lactate dehydrogenase. This includes residues that define the substrate and cofactor binding sites. Nevertheless, parasite lactate dehydrogenase exhibits high specificity for pyruvic acid, even more restricted than the specificity of human lactate dehydrogenases M4 and H4. Parasite lactate dehydrogenase exhibits high catalytic efficiency in the reduction of pyruvate, kcat/Km = 9.0 x 10(8) min(-1) M(-1). Parasite lactate dehydrogenase also exhibits similar cofactor specificity to the human isoforms in the oxidation of L-lactate with NAD+ and with a series of NAD+ analogs, suggesting a similar cofactor binding environment in spite of the numerous amino acid differences. Parasite lactate dehydrogenase exhibits an enhanced kcat with the analog 3-acetylpyridine adenine dinucleotide (APAD+) whereas the human isoforms exhibit a lower kcat. This differential response to APAD+ provides the kinetic basis for the enzyme-based detection of malarial parasites. A series of inhibitors structurally related to the natural product gossypol were shown to be competitive inhibitors of the binding of NADH. Slight changes in structure produced marked changes in selectivity of inhibition of lactate dehydrogenase. 7-p-Trifluoromethylbenzyl-8-deoxyhemigossylic acid inhibited parasite lactate dehydrogenase, Ki = 0.2 microM, which was 65- and 400-fold tighter binding compared to the M4 and H4 isoforms of human lactate dehydrogenase. The results suggest that the cofactor site of parasite lactate dehydrogenase may be a potential target for structure-based drug design.     

Riedel's thyroiditis: a case report and review of the literature

Riedel's thyroiditis is a very rare disease of unknown aetiology, occasionally associated with retroperitoneal and mediastinal fibrosis. It is a benign condition, but may be confused with an anaplastic carcinoma of the thyroid. The differential diagnosis with anaplastic carcinoma is assured only by intraoperative biopsy. The Authors report a clinical case: symptoms were a progressive enlargement of the thyroid gland, left recurrential palsy, dyspnoea and dysphagia. The surgical treatment was total thyroidectomy, performed with bilateral neurolysis of recurrent nerves. The patient was also under adjuvant corticosteroid treatment.     

Amino acid substitutions in the C-terminal regulatory domain disrupt allosteric effector binding to biosynthetic threonine deaminase from Escherichia coli

Shifts in the sigmoidal kinetics of allosteric threonine deaminase promoted by isoleucine and valine binding control branched chain amino acid biosynthesis in Escherichia coli. A highly conserved alpha-helix in the C-terminal regulatory domain of the tetrameric enzyme was previously implicated in effector binding and feedback inhibition. Double (447, 451) and triple (447, 451, 454) alanine replacements for the conserved amino acids leucine 447, leucine 451, and leucine 454 in this region yield enzyme variants that show increased sigmoidality in steady-state kinetics, and which are less sensitive to the allosteric modifiers isoleucine and valine. Equilibrium binding studies using fluorescence, enzyme kinetic, and calorimetric approaches indicate that the enzyme variants possess reduced affinity for isoleucine and valine, and suggest that heterotropic ligands can bind to the same site to promote their different effects. The increase in sigmoidal kinetics for the mutants relative to wild-type threonine deaminase may be attributable to the elimination of L-threonine binding to the effector sites, which activates the wild-type enzyme. Enzyme kinetic data and isotherms for active site ligand binding to the mutants can be analyzed in terms of a simple two-state model to yield values for allosteric parameters that are consistent with previous estimates based on an expanded two-state model for homotropic cooperativity for threonine deaminase.     

Elevated plasma osteopontin in metastatic breast cancer associated with increased tumor burden and decreased survival

Osteopontin (OPN) is a secreted, integrin-binding phosphoprotein that has been implicated in both normal and pathological processes; qualitative increases in OPN blood levels have been reported in a small number of patients with metastatic tumors of various kinds. We measured plasma OPN levels in 70 women with known metastatic breast carcinoma, 44 patient controls who were on follow-up after completion of adjuvant treatment for early breast cancer, and 35 normal volunteers. The median plasma OPN of patients with metastatic disease was 142 microgram/liter (range, 38-1312 microgram/liter) and was significantly different (P < 0.0001, Mann Whitney U test) from both control groups (medians, 60 and 47 microgram/liter; ranges, 15-117 and 22-122 microgram/liter). Furthermore, we found that increasing plasma OPN is associated with shorter survival (P < 0.001) when patients were grouped in terciles for plasma OPN. This was also demonstrated when using a Cox proportional hazards model. Median plasma OPN levels were significantly increased for three or more sites of involvement (median, 232 microgram/liter; n = 13) versus 1 or 2 metastatic sites (medians, 129 and 130 microgram/liter; n = 29 and 28, respectively). Plasma OPN levels were correlated with other biochemical markers related to the extent of disease, such as serum alkaline phosphatase, aspartate succinate aminotransaminase, and albumin (r = 0.81, 0.62, and -0.56, respectively; all P < 0.001). This study demonstrates a statistically significant elevation in plasma OPN in the majority ( approximately 70%) of a large series of patients with metastatic breast cancer when compared (95th percentile) to healthy women or patients who had completed adjuvant treatment for early-stage breast cancer. Furthermore, this is the first study to demonstrate that higher OPN levels in patients with metastatic breast cancer may be associated with an increased number of involved sites and decreased survival.     

Evidence for a role of a perferryl-oxygen complex, FeO3+, in the N-oxygenation of amines by cytochrome P450 enzymes

Two epithelial tumour lines, HeLa and KB, were treated with okadaic acid and calyculin A, specific inhibitors of Ser/Thr phosphatases (PP), esp. PP1 and PP2A. Morphological criteria, analysis of DNA fragmentation and studies of membrane integrity revealed that both agents concentration- and time-dependently induced apoptosis at nanomolar concentrations which in these cells was associated with the stimulation of a transglutaminase activity. Since a non-functional derivative of okadaic acid did not affect cell viability apoptosis was apparently related to the inhibition of PP1 and PP2A. Membrane damage marker activity was delayed by at least 24 h when compared to nuclear alterations.