The probability of causation under a stochastic model for individual risk

In this paper we offer a mathematical definition for the probability of causation that formalizes the legal and ordinary-language meaning of the term. We show that, under this definition, even the average probability of causation among exposed cases is not identifiable from epidemiologic data. This is because the probability of causation depends both on the unknown mechanisms by which exposure affects disease risk and competing risks, and on the unknown degree of heterogeneity in the background disease risk of the exposed population. We derive the maximum and minimum values for the probability of causation consistent with the observable population quantities. We also derive the relationship of the "assigned share" (excess incidence rate as a proportion of total incidence rate) to the probability of causation.     

DNA repair replication by soluble extracts from human lymphoid cell lines

A system is described in which extracts from human cells can perform repair replication on DNA damaged by ultraviolet light or chemical carcinogens. Whole cell extracts from lymphoid cell lines are incubated with damaged plasmid DNA circles at 30 degrees C in the presence of ATP and the four deoxynucleoside triphosphates. Repair synthesis is monitored by the incorporation of alpha-32P-dATP into closed circular plasmid molecules. Analysis of the time course of the reaction suggests that the slowest step in repair is incision, rather than polymerization or ligation. The size of repair patches inserted into ultraviolet-irradiated DNA during a reaction was estimated by substitution of thymidine triphosphate with 5-bromodeoxyuridine triphosphate and sedimentation in alkaline cesium chloride gradients. Patches with heterogeneous sizes of less than 120 bases were observed.     

Abrogation of antibody responses in rats to murine monoclonal antibody 791T/36 by treatment with daunomycin-cis-aconityl-791T/36 conjugates

Summary The majority of monoclonal antibodies in clinical use are of murine origin. It is now well-established that patients generate an antibody response to the mouse immunoglobulin which restricts repeated administration. Pre-sensitization of patients to mouse antibody is screened by hypersensitivity to i.d. administered antibody. This study shows that low doses of mouse antibody administered either i.d. or s.c. are highly immunogenic and suggests that a serological assay would be a safer method of screening for anti-mouse antibodies. Rats treated with monoclonal antibody linked via an acid labile cis-aconityl bond to daunomycin failed to produce a primary response to this conjugate. They were also rendered immunologically unresponsive to subsequent challenges with the unconjugated monoclonal antibody. The induced state of immunological unresponsiveness to free antibody persisted in the rats for 18 weeks and although antibody-cis-aconityl-daunomycin pre-treated animals eventually responded to the fourth challenge with free antibody, at week 25, the response was still significantly less than in the free antibody-pre-treated and challenged animals. These studies show that the use of antibody-cis-aconityl-duanomycin conjugates may provide an approach for the control of human responses to mouse immunoglobulin.     

5''-S-(2-aminoethyl)-N6-(4-nitrobenzyl)-5''-thioadenosine (SAENTA), a novel ligand with high affinity for polypeptides associated with nucleoside transport. Partial purification of the nitrobenzylthioinosine-binding protein of pig erythrocytes by affinity chromatography.

Derivatives of N6-(4-aminobenzyl)adenosine (substituted at the aminobenzyl group) and 5'-linked derivatives of N6-(4-nitrobenzyl)adenosine (NBAdo) were evaluated as inhibitors of site-specific binding of [3H]nitrobenzylthioinosine (NBMPR) to pig erythrocyte membranes. Potent inhibitors were SAENTA [5'-S-(2-aminoethyl)-N6-(4-nitrobenzyl)-5'-thioadenosine] and acetyl-SAENTA (the 2-acetamidoethyl derivative of SAENTA). SAENTA was coupled to derivatized agarose-gel beads (Affi-Gel 10) to form an affinity matrix for chromatographic purification of NBMPR-binding polypeptides, which in pig erythrocytes are part of, or are associated with, the equilibrative nucleoside transporter. When pig erythrocyte membranes were solubilized with octyl glucoside (n-octyl beta-D-glucopyranoside) and applied to SAENTA-Affi-Gel 10 (SAENTA-AG10), polypeptides that migrated as a broad band on SDS/PAGE with an apparent molecular mass of 58-60 kDa were selectively retained by the affinity gel. These polypeptides were identified as components of the nucleoside transporter of pig erythrocytes by reactivity with a monoclonal antibody (mAb 11C4) that recognizes the NBMPR-binding protein of pig erythrocytes. Retention of the immunoreactive polypeptides by SAENTA-AG10 was blocked by NBAdo. The immunoreactive polypeptides were released from SAENTA-AG10 by elution under denaturing conditions with 1% SDS or by elution with detergent solutions containing competitive ligands (NBAdo or NBMPR). A 72-fold enrichment of the immunoreactive polypeptides was achieved by a single passage of solubilized, protein-depleted membranes through a column of SAENTA-AG10, followed by elution with detergent solutions containing NBAdo. These results demonstrate that polypeptide components of NBMPR-sensitive nucleoside-transport systems may be partly purified by affinity chromatography using gel media bearing SAENTA groups.     

The chicken H5 gene is unlinked to core and H1 histone genes

An H5 cDNA clone was used to select H5 genomal recombinants from a chicken Charon 4A library. DNA sequence analysis shows that the H5 gene contains no introns. Putative 5′ promoter elements and a 3′ polyadenylation site are present within the 1.8 kb of DNA examined. Analysis of 41 kb of DNA surrounding the H5 gene shows that it is not closely linked to either H1 or core histone genes.     

The chemistry of the collagen cross-links. The mechanism of stabilization of the reducible intermediate cross-links.

The periodate-degradation technique was used to demonstrate the mechanism by which the reducible cross-links of collagen are stabilized. In all the tissues examined, Smith degradations of the 3H-labelled cross-links indicated that dihydroxylysinonorleucine is derived solely from hydroxylysino-5-oxonorleucine, the Amadori-rearranged product of the original condensation reaction. Monohydroxylysinonorleucine exists in both keto and aldimine forms, the former being derived from hydroxyallysine and the latter from allysine. Their relative proportions are tissue-dependent and are related to the degree of hydroxylation of the specific lysine residues in both the telopeptides and the triple helix.     

2-substituted derivatives of adenosine and inosine cyclic 3',5'-phosphate. Synthesis, enzymic activity, and analysis of the structural requirements of the binding locale of the 2-substituent on bovine brain protein kinase.

A number of 2-substituted cyclic nucleotide derivatives were synthesized and investigated as activators of cAMP-dependent protein kinase and as substrates for and inhibitors of cAMP phosphodiesterase. Ring closure of 5-amino-1-beta-D-ribofuranosylimidazol-4-carboxamide cyclic 3',5'-phosphate (1) with various aldehydes according to a new procedure (Meyer, R. B., Jr., Shuman, D.A., and Robins, R. K. (1974), J. Am. Chem. Soc. 96, 4962) gave new derivatives of adenosine cyclic 3',5'-phosphate with the following 2-substituents: n-propyl, n-hexl, n-octyl, n-decyl, styryl, o-methoxyphenyl, and 2-thienyl. Alkylation of 2-mercaptoadenosine cyclic 3',5'-phosphate (20, Meyer et al., 1974) gave new cAMP derivatives with the following 2-substituent: ethylthio, n-propylthio, isopropylthio, allylthio, n-decylthio, and benzylthio. Deamination of 2-methyl-,2-n-butyl-, and 2-ethylthioadenosine cyclic 3',5'-phosphate. Using multiple regression analysis, a striking relationship was found between the relative potency of the compounds as activators of bovine brain cAMP-dependent protein kinase and parameters describing the hydrophobic, steric, and electronic character of the substituents on these compounds. All compounds were substrates for a cyclic nucleotide phosphodiesterase preparation from rabbit kidney. Additionally, the compounds were as a group, good inhibitors of the hydrolysis of cAMP by phosphodiesterase preparations from rabbit lung, beef heart, and dog heart.     

Improved and large-scale synthesis of certain glycosyl cyanides. Synthesis of 2,5-anhydro-5-thio-D-allononitrile

The first synthesis of 2,5-anhydro-5-thio-D-allononitrile starting with L-lyxose, via a trifluoromethanesulfonic ester intermediate, has been accomplished. Methods have been developed to achieve a large-scale synthesis of 3,4,5,7-tetra-O-acetyl-2,6-anhydro-D-glycero-D-talo-heptononitrile (5). An improved procedure has been developed to synthesize 2,5-anhydro-3,4,6-tri-O-benzoyl-D-gulononitrile (9). The structures of 5 and the thioamide derivative from 9, 2,5-anhydro-3,4,6-tri-O-benzoyl-D-gulonothioamide, were confirmed by X-ray crystallographic analysis.     

The effects of immobilization on the biochemical,physiological and morphological features of Anabaena azollae

Anabaena azollae, a presumptive isolate from Azolla filiculoides, was immobilized in polyurethane foam, hydrophilic polyvinyl foam and alginate. When viewed by low-temperature scanning electron microscopy a thick mucilage layer covered the surface of both cells and matrix; this closely resembles the mode of attachment of the symbiont Anabaena in the Azolla leaf cavity. The heterocyst frequency of the immobilized A. azollae doubled relative to free-living cells and reached a level of 14–17%. Immobilization induced increases in both hydrogen production via nitrogenase or hydrogenase and in the rates and stabilization of acetylene reduction (N₂-fixation). Ammonia production by immobilized cells with L-methionine-D,L-sulfoximine (MSX) is greater than that of freeliving cells. Immobilized cells without MSX were, however, able to excrete ammonium at lower rates thus emulating the characteristic of the symbiotic cyanobacteria (A. azollae) in the leaf cavity of Azolla.Abbreviations Chl chlorophyll - GS glutamine synthetase - MSX L-methionine-D,L-sulfoximine - SEM scanning electron microscopy - PU polyurethane - PV polyvinyl     

Induced maturation of the human promyelocytic leukemia cell line, HL-60, by 2-beta-D-ribofuranosylselenazole-4-carboxamide

The new synthetic nucleoside analogue, 2-beta-D-ribofuranosylselenazole-4-carboxamide, was evaluated for its effects upon the growth and maturation of the human promyelocytic leukemia cell line, HL-60. At a concentration of greater than or equal to 1 nm, this agent was found both to decrease HL-60 cell proliferation and to cause the cells to acquire an ability to phagocytose opsonized yeast and to reduce nitroblue tetrazolium dye, functions characteristic of mature myeloid cells. In addition, this agent at similar concentrations caused a marked depression of intracellular guanosine nucleotide pools and a reduction in the incorporation of [14C] hypoxanthine into guanylates. These results suggested that the selenazole nucleoside caused an inhibition of inosinate monophosphate dehydrogenase, a key enzyme of guanylate biosynthesis. We therefore measured the activity of this enzyme indirectly by simultaneous-UV-radioactivity HPLC as well as by a direct radiometric method and demonstrated markedly reduced enzyme activities by both assays in drug treated cells. Dose response studies indicated that concentrations of drug which caused greater than 30% inhibition of IMP dehydrogenase activity induced greater than 50% maturation of the cells. These observations with this new nucleoside analogue provide further support for the concept that production of guanosine nucleotides and the activity of IMP dehydrogenase have a role in regulating the terminal maturation of myeloid cells.