Ligand-binding proteins: their potential for application in systems for controlled delivery and uptake of ligands.
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Unstable or harmful agents, such as drugs, vitamins, flavors, pheromones, and catalysts, for use in pharmaceutics, personal care, functional foods, crop protection, laboratories, offices, and industrial processes, require stabilization against oxidation and degradation or shielding from sensitive environments. Therefore, binding them to carriers with high affinity and selectivity for targeting to the right environment and subsequent controlled release is beneficial, especially if this allows improved control of (stimulus-induced) release. Proteins often possess one or more of these properties, whereas modern biotechnology and bioinformatics provide an increasing number of tools to engineer and adapt these properties. Carrier systems are now developed that incorporate proteins as the central ligand-binding component, e.g., lectins for glucose-triggered release of glycosylated insulin and bispecific antibodies for brain targeting of drugs, but ligand-binding proteins can potentially be used in many other applications. Collectively, the proteins available in nature bind an impressive variety of ligands and non-natural analogs. In this light, various ligand-binding protein classes are surveyed, including biotin-, lipid-, immunosuppressant-, insect pheromone-, phosphate-, and sulfate-binding proteins, as well as bacterial periplasmic proteins, lectins, serum albumins, immunoglobulins, and inactivated enzymes. Disadvantages, such as enzymatic degradation or immunogenicity, associated with the pharmaceutical use of certain proteins can be avoided by incorporating these proteins in more complex carrier and targeting systems. In other applications, this may not be necessary. The enclosure of high-affinity (potentially stimulus-sensitive) binding proteins within an envelope that acts as a diffusion barrier for the ligand may provide excellent slow release. Many possibilities seem to be as yet unexplored. (+info)
DNA delivery by phage as a strategy for encapsulating toroidal condensates of arbitrary size into liposomes.
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We report a strategy for encapsulating and condensing DNA. When T5 phage binds to its membrane protein receptor, FhuA, its double stranded DNA (120,000 bp) is progressively released base pair after base pair in the surrounding medium. Using cryoelectron microscopy, we have visualized the structures formed after T5 phage DNA is released into neutral unilamellar proteoliposomes reconstituted with the receptor FhuA. In the presence of spermine, toroidal condensates of circumferentially wrapped DNA were formed. Most significantly, the sizes of these toroids were shown to vary, from 90 to 200 nm in their outer diameters, depending on the number of DNA stands transferred. We have also analyzed T5 DNA release in bulk solution containing the detergent-solubilized FhuA receptor. After DNA release in a spermine containing solution, huge DNA condensates with a diameter of about 300 nm were formed containing the DNAs from as many as 10-20 capsids. At alkaline pH, the condensates appeared as large hollow cylinders with a diameter of 200 nm and a height of 100-200 nm. Overall, the striking feature of our experiments is that, because of the progressive release of DNA from the phage capsid, the mechanism of toroid formation is fundamentally different from that in the classical studies in which highly dilute, "naked" DNA is condensed by direct addition of polyvalent cations; as a consequence, our method leads to toroids of arbitrary size. (+info)
Cp50 of propofol with and without nitrous oxide 67%.
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The target concentration of propofol required to prevent response to surgical incision was determined in 60 unpremedicated ASA I or II patients, who breathed either oxygen-enriched air or nitrous oxide 67% in oxygen. Propofol was infused using a target-controlled infusion system incorporating the standard 'Diprifusor' pharmacokinetic model, with the target concentration for each patient decided by up/down sequential allocation. Presence or absence of movement in response to a groin incision was determined by the surgeon. The calculated blood concentration at which 50% of patients responded (Cp50calc), determined by probit analysis, was 6.8 micrograms ml-1 for patients who breathed oxygen-enriched air and 4.9 micrograms ml-1 for those who breathed nitrous oxide 67% in oxygen. (+info)
The exacerbating effect of insulin-induced hypoglycemia on spontaneous peripheral neuropathy in aged B6C3F1 mice.
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The effect of insulin-induced hypoglycemia on spontaneous peripheral neuropathy in aged mice was examined. Ninety-five-week-old female B6C3F1 mice were infused subcutaneously for 2 weeks with 40 or 80 IU/kg/day of insulin with a micro osmotic pump. Blood glucose level was decreased during the infusion (4.3-6.8 mmol/L in mice receiving 40 IU/kg/day of insulin or 2.4-5.4 mmol/L in mice receiving 80 IU/kg/day of insulin versus 6.5-7.6 mmol/L in control mice). In histopathological examination, axonal degeneration and/or remyelination were observed in a small number of nerve fibers of control mice. Similar nerve fiber lesions were observed in mice receiving 40 IU/kg/day of insulin, whereas severer lesions with an increase in segmental axonal degeneration of nerve fibers were observed in 4/7 mice receiving 80 IU/kg/day of insulin. These findings suggest that spontaneous peripheral neuropathy in aged mice is exacerbated by sustained hypoglycemia induced by insulin treatment. (+info)
Pegylated liposomes have potential as vehicles for intratumoral and subcutaneous drug delivery.
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The potential value of intratumoral or s.c. injections of pegylated liposomes as locoregionally targeted therapy of tumors and their draining lymph nodes was assessed in nude mice as part of an ongoing program aimed at developing pegylated liposomal radiosensitizers for the treatment of head and neck cancers. Animals received (111)In-labeled diethylenetriaminepentaacetic acid (DTPA), either encapsulated in pegylated liposomes (IDLPL) or in the unencapsulated form ((111)In-DTPA), as intratumoral or s.c. injections, and the local retention, locoregional nodal drainage, and systemic biodistribution were measured. After intratumoral injections, IDLPL were effectively retained in the tumor with an area under the curve (AUC) between 1 and 96 h of 2,574.4% injected dose per gram hours (%ID/g x h). The corresponding value for (111)In-DTPA was 204.4%ID/g x h. Accumulation of IDLPL was seen in ipsilateral lymph nodes. The maximal ipsilateral:contralateral node ratios were 8:1 (2.2 versus 0.27%ID/g) for inguinal nodes at 24 h and 19:1 (2.5 versus 0.13%ID/g) for axillary nodes at 48 h. Unencapsulated (111)In-DTPA showed no evidence of accumulation in locoregional nodes. After s.c. injection, IDLPL were cleared slowly from the injection site with an AUC between 1 and 192 h of 24,051.1%ID/g x h. Unencapsulated (111)In-DTPA was cleared rapidly with an AUC between 1 and 192 h of 46.4%ID/g x h. Again, significant levels of IDLPL were detected in the ipsilateral locoregional nodes, with ipsilateral:contralateral ratios of 121:1 (57.9 versus 0.48%ID/g) at 24 h (inguinal nodes) and 17:1 (5.2 versus 0.3%ID/g) at 72 h (axillary nodes). There was no retention of unencapsulated (111)In-DTPA in the draining nodes. Locoregional administration of pegylated liposomal radiosensitizers may be a useful approach for targeted therapy of head and neck tumors and their nodal metastases. (+info)
Comparative efficacy and distribution of lipid formulations of amphotericin B in experimental Candida albicans infection of the central nervous system.
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The central nervous system (CNS) distribution and antifungal efficacy of all 4 approved formulations of amphotericin B (AmB) were investigated in a rabbit model of hematogenous Candida albicans meningoencephalitis. Treatment with AmB deoxycholate (1 mg/kg/day) or liposomal AmB (5 mg/kg/day) yielded the highest peak plasma concentration (C(max)), area under concentration versus time curve from zero to 24 h (AUC(0-24)), and time during dosing level tau Ttau>minimum inhibitory complex (MIC) values and led to complete eradication of C. albicans from brain tissue (P<.05 vs. untreated controls). By comparison, AmB colloidal dispersion and AmB lipid complex (5 mg/kg/day each) were only partially effective (not significant vs. untreated controls). There was a strong correlation of C(max), AUC(0-24), C(max)/MIC, AUC(0-24)/MIC, and Ttau>MIC with clearance of C. albicans from brain tissue (P+info)
Biodistribution and pharmacokinetics of 111In-DTPA-labelled pegylated liposomes in a human tumour xenograft model: implications for novel targeting strategies.
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The biodistribution and pharmacokinetics of 111In-DTPA-labelled pegylated liposomes in tumour-bearing nude mice was studied to examine possible applications of pegylated liposome-targeted anti-cancer therapies. Nude mice received an intravenous injection of 100 microl of 111In-DTPA-labelled pegylated liposomes, containing 0.37-0.74 MBq of activity. The t1/2alpha and t1/2beta of 111In-DTPA-labelled pegylated liposomes were 1.1 and 10.3 h, respectively. Tumour uptake was maximal at 24 h at 5.5 +/- 3.0% ID g(-1). Significant reticuloendothelial system uptake was demonstrated with 19.3 +/- 2.8 and 18.8 +/- 4.2% ID g(-1) at 24 h in the liver and spleen, respectively. Other sites of appreciable deposition were the kidney, skin, female reproductive tract and to a lesser extent the gastrointestinal tract. There was no indication of cumulative deposition of pegylated liposomes in the lung, central nervous system, musculoskeletal system, heart or adrenal glands. In contrast, the t1/2alpha and t1/2beta of unencapsulated 111In-DTPA were 5 min and 1.1 h, respectively, with no evidence of accumulation in tumour or normal tissues. Incubation of 111In-DTPA-labelled pegylated liposomes in human serum for up to 10 days confirmed that they are very stable, with only minor leakage of their contents. The potential applications of pegylated liposomes in the arena of targeted therapy of solid cancers are discussed. (+info)
Fractals and cancer.
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Recent studies have shown that fractal geometry, a vocabulary of irregular shapes, can be useful for describing the pathological architecture of tumors and, perhaps more surprisingly, for yielding insights into the mechanisms of tumor growth and angiogenesis that complement those obtained by modern molecular methods. This article outlines the basic methods of fractal geometry and discusses the value and limitations of applying this new tool to cancer research. (+info)