Mutant PCNA alleles are associated with cdc phenotypes and sensitivity to DNA damage in fission yeast

Twenty-eight site-directed mutations were introduced into the fission yeast gene (pcn1+) that encodes proliferating cell nuclear antigen (PCNA) and their in vivo effects analyzed in a strain with a null pcn1 background. Mutants defective in enhancing processivity of DNA polymerase delta have previously been identified. In this study, we assessed all of the mutants for their sensitivities to temperature, hydroxyurea, UV irradiation and methyl methanesulfonate (MMS), and specific mutants were also tested for sensitivity to gamma irradiation. One cold-sensitive allele, pcn1-3, was characterized in detail. This mutant had a recessive cold-sensitive cdc phenotype and showed sensitivity to hydroxyurea, UV, and gamma irradiation. At the non-permissive temperature pcn1-3 protein was able to form homotrimers in solution and showed increased stimulation of both synthetic activity and processivity of DNA polymerase delta relative to the wild-type Pcn1+ protein. Epistasis analyses indicated that pcn1-3 is defective in the repair pathway involving rad2+ but not defective in the classical nucleotide excision repair pathway involving rad13+. Furthermore, pcn1-3 is either synthetically or conditionally lethal in null checkpoint rad backgrounds and displays a mitotic catastrophe phenotype in these backgrounds. A model for how pcn1-3 defects may affect DNA repair and replication is presented.     

Magnetic resonance images of neuronal migration anomalies

Neuronal migration anomalies are a spectrum of brain malformations caused by insults to migrating neuroblasts during the sixth week to fifth month of gestation. To study the characteristics of MRI findings in migration anomalies, MR images of 36 patients (28 children and 8 adults) with migration anomalies were evaluated. Five patients had lissencephaly, eight had pachygyria, twelve had schizencephaly, six had heterotopias of gray matter, three had hemimegalencephaly, and two had polymicrogyria. The frequency of migration anomalies was 0.51% of all cranial MRI studies and 1.21% of pediatric cranial MRI studies at our hospital. The major clinical presentations of these patients were seizure (64%), development delay (42%), motor deficits (42%) and mental retardation (25%). Twenty-five patients (69%) associated with other brain anomalies, including: other migration anomalies in 12 cases (33%), absence of the septum pellucidum in 10 cases (28%), Dandy-Walker malformation/variant in 5 cases, arachnoid cyst in 4 cases, agenesis of the corpus callosum in 3 cases, holoprosencephaly in 2 cases, mega cisterna magna in 1 case and cephalocele in 1 case. Some of them presented with multiple complicated anomalies. As MR imaging provides superb gray-white matter distinction, details of cortical anatomy and multiplanar capability, it can clearly delineate the detail morphologic changes of the brain caused by neuronal migration disorders as well as the associated anomalies.     

Evaluation of atypical cytochrome P450 kinetics with two-substrate models: evidence that multiple substrates can simultaneously bind to cytochrome P450 active sites

Some cytochrome P450 catalyzed reactions show atypical kinetics, and these kinetic processes can be grouped into five categories: activation, autoactivation, partial inhibition, substrate inhibition, and biphasic saturation curves. A two-site model in which the enzyme can bind two substrate molecules simultaneously is presented which can be used to describe all of these observed kinetic properties. Sigmoidal kinetic characteristics were observed for carbamazepine metabolism by CYP3A4 and naphthalene metabolism by CYPs 2B6, 2C8, 2C9, and 3A5 as well as dapsone metabolism by CYP2C9. Naphthalene metabolism by CYP3A4 and naproxen metabolism by CYP2C9 demonstrated nonhyperbolic enzyme kinetics suggestive of a low Km, low Vmax component for the first substrate molecule and a high Km, high Vmax component for the second substrate molecule. 7, 8-Benzoflavone activation of phenanthrene metabolism by CYP3A4 and dapsone activation of flurbiprofen and naproxen metabolism by CYP2C9 were also observed. Furthermore, partial inhibition of 7, 8-benzoflavone metabolism by phenanthrene was observed. These results demonstrate that various P450 isoforms may exhibit atypical enzyme kinetics depending on the substrate(s) employed and that these results may be explained by a model which includes simultaneous binding of two substrate molecules in the active site.     

Aristolochic acids, aristolactam alkaloids and amides from Aristolochia kankauensis

Fourteen aristolochic acid derivatives: ariskanins A-E, 3-hydroxy-4-methoxy-10-nitrophenanthrene-1-carboxylic acid methyl ester, aristolochic acid-II methyl ester, aristolochic acid-IV methyl ester, aristolochic acid-C, -I, -II, -III, -IV, -IVa; nine aristolactam alkaloids: aristolactam, aristolactam-AII, -BIII, -AIII, -III, cepharanone-A, 9-methoxy-aristolactam-I, aristolactam-N-beta-D-glucoside and aristolactam-C-N-beta-D-glucoside; a 4,5-dioxoaporphine alkaloid: cepharadione-A, together with 12 other compounds: methyl-p-coumarate, N-trans-feruloyltyramine, N-cis-feruloyltyramine, methyl vanillate, methyl paraben, allantoin, an octadecyl- and eicosyl ferulate mixture, cis- and trans-p-coumaric acid, N-p-coumaroyltyramine, N-p-cis-coumaroyltyramine, methyl ferulate and isorhamnetin-3-O-rutinoside were isolated and characterized from the fresh root and stem of Aristolochia kankauensis. Their structures were elucidated by spectral and chemical methods. Among them, ariskanins-A-E and N-p-cis-coumaroyltyramine are reported for the first time from a natural source. The cytotoxicity and antiplatelet activity of the compounds isolated are also discussed.     

A comparison between the Fick method and indirect calorimetry for determining oxygen consumption in patients with fulminant hepatic failure

OBJECTIVE: To compare the Fick method of determining oxygen consumption (VO2) with a gas exchange method in a group of patients in whom the cardiac output and mixed venous oxygen saturation values were consistently high. DESIGN: A prospective, observational study. SETTING: A ten-bed intensive therapy unit at a university teaching hospital. PATIENTS: Seventeen patients suffering from fulminant hepatic failure who required ventilatory support and invasive hemodynamic monitoring. All patients were sedated and paralyzed throughout the study period. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: VO2 was determined simultaneously by indirect calorimetry and by the Fick method five or six times in each patient over a 5-hr period after resuscitation with fluids and, if clinically indicated, norepinephrine infusion. The agreement between the methods was poor (limits of agreement +19 to -101 mL/min/m2) and the Fick method consistently underestimated gas exchange measurements (mean bias 41 mL/min/m2). The bias varied widely, both between and within individual patients. The reproducibility of the Fick-derived VO2 was worse than the indirect calorimetry measurements, indicating that the dispersion of data attributable to measurement error was greater with the Fick method. CONCLUSIONS: Under clinical conditions, the agreement between Fick calculations and indirect calorimetry measurements of VO2 in hyperdynamic patients with fulminant hepatic failure was extremely poor. The reproducibility of Fick calculations was less than the reproducibility derived by gas exchange measurements because of the large measurement errors that may occur with the Fick method when the cardiac output is large and the arterial-venous oxygen content difference is small. Fick calculations systematically underestimate gas exchange measurements. The Fick method is inaccurate and unreliable when an estimation of VO2 is required in patients with this hemodynamic pattern.     

Epithalamin effects on carbohydrate metabolism and cardiovascular system in patients with non-insulin dependent diabetes mellitus

Epithelamine made in Russia (Samson, St. Petersburg) was tried for effects on carbohydrate metabolism and cardiovascular system in 33 patients with non-insulin-dependent diabetes mellitus (NIDDM). Adjuvant use of epithelamine in combined treatment of NIDDM promoted a stable compensation of carbohydrate metabolism, lowering of glycosylated hemoglobin, immunoreactive insulin. There was also a moderate hypotensive effect and improvement of left ventricular diastolic function.