Ciba Foundation symposium最新文献

Abundant evidence suggests a relationship between antibiotic resistance and use, including animal models, consistent associations between resistance and antibiotic use in hospitals, concomitant variation in resistance as antibiotic use varies, and a dose-response relationship for many pathogen/antibiotic combinations. Much of the evidence has come from studies performed in single hospitals. Most multicentre studies on resistance have not included data on antibiotic usage. Despite this substantial body of evidence, some studies have failed to demonstrate an association between antibiotic resistance and use, suggesting other contributing factors such as cross-transmission, inter-hospital transfer of resistance, a community contribution to resistance, or a complex relationship between resistance and the use of a variety of antibiotics. A multicentre study, project ICARE (Intensive Care Antimicrobial Resistance Epidemiology), implemented in 1994 by Centers for Disease Control and Prevention and Rollins School of Public Health, Emory University, has found dramatic differences in the patterns of antibiotic usage and resistance in US hospitals. The findings suggest that antibiotic usage is the major risk factor in development of antibiotic resistance in hospitals but the relationship can be complex with additional factors involved. Understanding the problem of antibiotic resistance in a hospital cannot be achieved without knowledge of the hospital's pattern of antibiotic use.

After large releases of radionuclides, exposure of the embryo or fetus can take place by external irradiation or uptake of radionuclides. The embryo and fetus are radiosensitive throughout prenatal development. The quality and extent of radiation effects depend on the developmental stage. During the preimplantation period (one to 10 days postconception, p.c.), a radiation exposure of at least 0.2 Gy can cause the death of the embryo. Malformations are only observed in rare cases when genetic predispositions exist. Macroscopic, anatomical malformations are induced only after irradiation during the major organogenesis (two to eight weeks p.c.). A radiation dose of about 0.2 Gy is a doubling dose for the malformation risk, as extrapolated from experiments with rodents. The human embryo may be more radioresistant. During early fetogenesis (8-15 weeks p.c.) a high radiosensitivity exists for the development of the brain. Radiation doses of 1.0 Gy cause severe mental retardation in about 40% of the exposed fetuses. It must be taken into account that a radiation exposure during the fetal period can also induce cancer. It is generally assumed that the risk exists at about the same level as for children.

Phosphodiester and phosphorothioate oligodeoxynucleotides are polyanions that cannot passively diffuse across cell membranes. Instead, the processes of adsorbtive endocytosis and pinocytosis probably account for the great majority of oligodeoxynucleotide internalization in most cell types. Oligodeoxynucleotides can adsorb to heparin-binding, cell surface proteins. An example of such a protein is the integrin Mac-1 (alpha M beta 2; CR3; CD11b/CD18), a receptor for fibrinogen which is found on neutrophils, macrophages and natural killer cells. Up-regulation of neutrophil cell surface Mac-1 expression by interleukin 8, arachidonic acid or tumour necrosis factor alpha leads to increased cell surface oligodeoxynucleotide binding and internalization. Binding and internalization can be blocked by both fibrinogen and by anti-Mac-1 monoclonal antibodies. Subsequent to internalization, oligodeoxynucleotides reside in subcellular vesicular structures, i.e. endosomes and lysosomes. However, in the absence of permeabilizing agents, these compartments may be sites of sequestration and the oligomers may be unavailable for antisense activity. At present, controversy surrounds the use of guanosine-rich phosphorothioate oligodeoxynucleotides as antisense agents. We examined the ability of the 24mer antisense rel A (p65) phosphorothioate oligodeoxynucleotide to inhibit nuclear translocation of NF kappa B in K-BALB murine fibroblasts. 7-Deaza-2'-deoxyguanosine substitution in the 5' guanosine quartet region demonstrated that inhibition of nuclear translocation could not be due to a Watson-Crick antisense effect. Rather, we favour the explanation that the parent molecule may be a sequence-specific, apatameric decoy.

The need to maintain self-tolerance is at odds with the need to draw upon antibody and T cell receptor diversity to fight infection. Advances in genetic manipulation of the mouse have at last brought into view the clonal selection mechanisms that underpin self-tolerance, confirming in general terms the notion of clonal deletion and clonal anergy put forward by Burnet and Nossal. The image that has emerged, however, is much more sophisticated than could have been imagined, revealing that self-reactive clones are deleted or held back in a remarkable series of culling checkpoints placed at many steps along the pathway to antibody production. These checkpoints act in concert to balance the nature and size of the holes in the repertoire generated by self-tolerance against the need to draw upon as many clones as possible for immunity to infection. Spontaneous and induced mutations in the mouse, such as Fas, PTP1C and CD45 mutations, have just begun to yield a few glimpses into the molecular circuitry underpinning these cellular checkpoints. Much more extensive genetic analysis, made possible by the genome project, will be needed to illuminate the details of those circuits and the factors that lead them to fail in autoimmune disease.

Antimicrobial resistance is becoming an important public health problem for both hospital- and community-acquired infections. In the hospital, infections caused by drug-resistant Staphylococcus aureus, Mycobacterium tuberculosis, enterococci, and a variety of Gram-negative rods are resulting in increased morbidity, mortality and costs, in part because of prolonged hospitalization and the use of more expensive antimicrobial agents. Drug-resistant, community-acquired infections are also causing important problems in both the developed and the developing world. Although the relative importance of specific pathogens varies with the geographical area, community-acquired pathogens including Salmonella, Shigella, Neisseria gonorrhoeae, Haemophilus influenzae and Streptococcus pneumoniae are causing both sporadic cases and outbreaks of drug-resistant illness. The emergence of antimicrobial resistance is being attributed to a series of societal, technological, environmental and microbial changes. These include increasing populations of susceptible hosts, international travel and commerce, changes in technology and industry, microbial adaptation and change, and the breakdown of public health measures. Addressing emerging problems and antimicrobial resistance will require enhanced surveillance, prudent use of existing antimicrobial drugs, development of new antimicrobial agents, increased emphasis on infection control and hygienic practices, effective disease control programs, better use of existing vaccines, and development of more and better vaccines.

Since the introduction of antibiotics in the late 1940s there has been an inexorable propagation of antibiotic resistance genes in bacterial pathogens (and their relatives). This survival phenomenon was first characterized as the appearance of point mutations that altered drug targets, but in the mid-1950s transmissible antibiotic resistance genes were reported in Japan. Since this time both resistance strategies have been used, often in concert. For some types of antibiotic, only resistance by mutation has been identified, for others only resistance by plasmid acquisition. There is conflicting evidence with respect to the presence of antibiotic resistance in bacterial pathogens in the 'pre-antibiotic' era; however, it is likely that the evolution of antibiotic resistance occurred over short periods. Thus, antibiotic resistance gene must be common in the environment, but their derivation remains to be established conclusively. This paper examines the proposals that antibiotic resistance genes originated in the bacterial population, either as bona fide resistance genes or genes encoding metabolic functions. In addition, the acquisition of heterologous resistance determinants by different genetic elements, their intergeneric exchange mechanisms, and the possible roles of antibiotics in the processes are discussed. Are there prospects for drug intervention that eliminate or retard these natural evolutionary processes?

There is considerable concern about possible links between ambient air pollution and the upward trend in asthma. This chapter reviews the mechanistic and epidemiological evidence concerning air pollution and asthma and examines the hypothesis that trends in asthma could be explained by air pollution. It is concluded that existing evidence is not sufficient to link air pollution with the initiation of asthma in healthy subjects. Although there is better evidence that air pollution can provoke or aggravate asthma, it probably plays a minor role at a public health level, in comparison with other factors. It is therefore unlikely that trends in asthma could be explained by air pollution. Furthermore, correlations between some air pollutants and asthma over time are not consistent with the hypothesis. The possibility of a specific effect of motor vehicle pollution needs further investigation but this factor is unlikely to be the main cause of the worldwide increase in asthma.

Following extensive screening of more than 50 antisense-designed phosphorothioate oligodeoxynucleotides targeted to human c-raf mRNA, one oligodeoxynucleotide (ISIS 5132/CGP 69846A) was identified as being the most potent inhibitor of c-raf gene expression both in vitro and in vivo. ISIS 5132 is a highly sequence-specific and target-specific inhibitor of c-raf mRNA and protein levels. c-raf inhibition results in dramatic alteration of downstream signalling events within the MAP kinase signalling pathway. Moreover, this oligodeoxynucleotide displays potent antitumour activity against a broad spectrum of tumour types in mouse models and has progressed to Phase I clinical trails. In an effort to identify potential back-up compounds to ISIS 5132, a variety of second-generation 2' sugar modifications have been evaluated for activity against c-raf in cell culture. We have identified a number of second-generation oligonucleotides with improved biophysical characteristics that result in enhanced activity against c-raf in cell culture. Activity enhancement was most pronounced for 2'-O-methoxyethyl-modified oligonucleotides and this modification also resulted in significantly improved antitumour activity in vivo.

Efficient process technologies for the preparation of 2'-substituted nucleoside monomers, as well as for oligonucleotide preparation, are introduced. A novel method for efficient preparation of 2'-substituted uridines is presented. This method employs the 3'-hydroxyl group of 2,2'-anhydrouridine as a tether for the facile intramolecular introduction of nucleophiles to the 2'-position. It allows access to 2'-alkoxy substituents from their alcohol precursors and to substituted 2'-amino substituents, such as the novel O-substituted 2'-hydroxylaminouridines. A novel process for large-scale oligonucleotide synthesis is discussed, which allows solution phase coupling of the monomer to the growing oligonucleotide chain. This is followed by selective isolation of productive coupling product by anchoring to a resin. Release from this resin completes a coupling cycle.