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Y K Oh

Publications and source records attributed to Y K Oh.

At least 37 records · Page 2Linked to original sources
PubMed1999

Enhanced hepatocyte uptake and liver targeting of methotrexate using galactosylated albumin as a carrier.

Liver targeting of drugs has wide therapeutic implications due to numerous liver-related diseases. Using conjugates of methotrexate (MTX) to variously galactosylated bovine serum albumin (BSA), we studied whether we could enhance the liver targeting of MTX, a model drug, via galactose receptors selectively abundant on the hepatocytes. Here, we report that the galactosylation of the carrier protein BSA significantly enhanced the hepatocyte uptake and liver targetability of MTX. In vitro, the amount of MTX taken up by rat hepatocytes was positively correlated with the galactose content in BSA. MTX conjugates were relatively stable in plasma, but released MTX with time in liver homogenates. These results imply that the conjugates would exert low toxicity in the blood, but have therapeutic activity in the liver by liberating MTX. In vivo, MTX-galactosylated BSA conjugates (MTX-L(24)BSA) showed significantly different pharmacokinetics from free MTX or MTX-BSA conjugates. The plasma level of free MTX rapidly declined in a biexponential fashion with an apparent terminal half-life of 0.35 h. MTX-BSA conjugates showed the slowest decline with an apparent terminal half-life of 6 h, whereas MTX-L(24)BSA showed a biphasic pattern; a rapid distributive phase with a half-life of 0.567 h and a slow terminal phase. MTX-L(24)BSA showed the highest liver targetability, when evaluated in terms of two indices based on the area under the total amount of radioactivity-time curve (AUQ); Te*(liver), % AUQ(liver) to total AUQ, and te*, the ratio of AUQ(liver) to AUQ(kidney). Compared with free MTX and MTX-BSA, MTX-L(24)BSA showed about twofold higher Te*(liver) of 87.5%. The te* of MTX-L(24)BSA was 25- and fourfold higher than those of free MTX and MTX-BSA, respectively. Moreover, MTX-L(24)BSA showed a gradual increase in the therapeutically active intact form of MTX in the liver while showing the lowest level of intact MTX in the kidney. These results suggest that galactosylated BSA has a great potential as an hepatocyte-directed and more effective liver targeting carrier of drugs for liver diseases.

Animals↗
PubMed1999

Pharmacodynamics of insulin in polyethylene glycol-coated liposomes.

To reduce the injection frequency and toxicity of intravenously administered protein drugs, it is necessary to develop safe and sustained injectable delivery systems. In this study, to evaluate liposomes as safe and sustained injectable delivery systems of proteins, we chose insulin as a model protein drug and tested its incorporation efficiency and pharmacodynamics in various liposomes with and without polyethylene glycol (PEG)-derivatized phospholipid. The liposomes coated with PEG showed 3-fold higher efficiency of insulin incorporation than did the liposomes without PEG. Moreover, among the liposomes coated with PEG, dipalmitoylphosphocholine (DPPC) liposomes showed higher incorporation efficiency than did dimyristoylphosphocholine (DMPC) liposomes. For pharmacodynamic study, insulin (2 IU/kg) was administered in various formulations, such as insulin alone in phosphate-buffered saline and insulin in the DPPC liposomes with and without PEG, to streptozotocin-treated diabetic rats. The pharmacodynamics of insulin alone, however, could not be measured due to the immediate death of rats caused by hypoglycemic shock. In contrast, all the rats treated with liposomal insulin survived, probably by the sustained release of insulin from liposomes. Pharmacodynamics of liposomal insulin showed that PEG-coated liposomes induced the lowest level of blood glucose-the nadir-1 h later than did the liposomes without PEG. These results indicate that PEG-coated liposomes could be developed as a relatively safe and sustained injectable delivery system for insulin with improved incorporation efficiency. Moreover, it is suggested that the liposomes coated with PEG might have a potential as safe injectable delivery systems for other protein and peptide drugs.

Animals↗
PubMed1999

Substance P augments nitric oxide production and gene expression in murine macrophages.

We investigated the effects of substance P (SP) on nitric oxide (NO) synthase activity in macrophages by measuring the production of nitrite and the expression of inducible NO synthase (iNOS) mRNA and protein. In LPS-activated macrophages, SP stimulated NO production in time and concentration dependent manners. These SP effects were blocked by a specific NK-1 receptor antagonist. Furthermore, SP stimulation increased the levels of both iNOS mRNA and iNOS protein. These results demonstrate that SP can increase LPS induced NO production in macrophages by augmenting the induction of iNOS expression. We also examined the role of SP on acute-cold stress induced altered production of NO by mouse peritoneal macrophages. SP enhanced the LPS-induced macrophages NO production from stressed mice relative to the non-stressed mice. These results suggest that SP may have an important modulatory role in production of NO by macrophages.

Animals↗
PubMed1999

Nuclear factor kappa B-mediated kainate neurotoxicity in the rat and hamster hippocampus.

Administration of the excitotoxin kainate produces seizure activity and selective neuronal death in various brain areas. We examined the degeneration pattern of hippocampal neurons following systemic injections of kainate in the hamster and the rat. As reported, treatment with kainate resulted in severe neuronal loss in the hilus and CA3 in the rat. While the hilar neurons were also highly vulnerable to kainate in the hamster, neurons in the CA1 area, but not CA3, were highly sensitive to kainate. In both animals, immunoreactivity to anti-p50 nuclear factor kappa B antibody was increased in nuclei of the hilar neurons within 4 h following administration of kainate. Kainate treatment also increased the nuclear factor kappa B immunoreactivity in hamster CA1 neurons and rat CA3 neurons 24 h later. Neurons showing intense nuclear factor kappa B signal were stained with acid fuchsin. Kainate also increased DNA binding activity of p50 and p65 nuclear factor kappa B in the nuclear extract of the hippocampal formation as analysed by electrophoretic mobility shift assay in the hamster, suggesting that activation of nuclear factor kappa B may contribute to kainate-induced hippocampal degeneration. Administration of 100 nmol dizocilpine maleate 3 h prior to kainate attenuated kainate-induced activation of nuclear factor kappa B and neuronal death in CA1 in the hamster. The present study provides evidence that the differential vulnerability of neurons in the rat and the hamster hippocampus to kainate is partly mediated by mechanisms involving N-methyl-D-aspartate-dependent activation of nuclear factor kappa B.

Animals↗
PubMed1999

Amycolatopsis thermoflava sp. nov., a novel soil actinomycete from Hainan Island, China.

A soil isolate, which had been assigned to the genus Nocardia, was shown to have properties consistent with its classification in the genus Amycolatopsis. An almost complete nucleotide sequence of the 16S rDNA of the strain was determined following cloning and sequencing of the amplified gene. The sequence was aligned with those available for members of the family Pseudonocardiaceae and related taxa and phylogenetic trees were inferred using three tree-making algorithms. The organism consistently formed a distinct monophyletic clade with the type strain of Amycolatopsis methanolica, but DNA-DNA relatedness data showed that the two strains belonged to distinct genomic species. The organism was also distinguished from the type strains of all validly described species of Amycolatopsis using a battery of phenotypic properties. The genotypic and phenotypic data show that the strain merits recognition as a new species of the genus Amycolatopsis. The name proposed for the new species is Amycolatopsis thermoflava sp. nov. The type strain is IFO 14333T.

Actinomycetales↗
PubMed1999

Stages I-III follicular lymphoma: role of CT of the abdomen and pelvis in follow-up studies.

PURPOSE: To evaluate the efficiency of axial computed tomography (CT) in detecting relapses of stage I, II, or III follicular lymphoma. MATERIALS AND METHODS: A total of 328 patients with previously untreated stage I, II, or III follicular lymphoma were treated between 1978 and 1994. Two hundred fifty-seven patients achieved complete response; 78 who relapsed form the basis of this study. Fifteen patients had stage I; 28, stage II; and 35, stage III disease. Fifteen patients underwent radiation therapy; 12, chemotherapy; and 51, radiation and chemotherapy. Medical records were reviewed to analyze the yield of abdominal and pelvic CT in detecting recurrence relative to the yield of standard clinical, hematologic, and imaging studies. A positive study was defined as one that led to or was abnormal at the diagnosis of recurrence. RESULTS: The median follow-up was 101 months. Eleven relapses were detected only at abdominal, pelvic, or both abdominal and pelvic CT. CONCLUSION: Fourteen percent (11 of 78) of the relapses were detected solely at abdominal and/or pelvic CT. Eleven (4.3%) of the 257 patients who achieved complete response benefited from abdominal and pelvic CT. The yield of the routine use of abdominal and pelvic CT in follow-up studies appears to be low for stages I-III follicular lymphoma.

Female↗
PubMed1997

The efficiency of antigen delivery from macrophage phagosomes into cytoplasm for MHC class I-restricted antigen presentation.

Macrophages can present exogenous antigen in association with MHC class I molecules. Indirect evidence indicates that antigens internalized by phagocytosis can enter cytoplasm before following the conventional MHC class I presentation pathway. However, little is known about how common such entry is, or to what extent it depends on the kind of particle ingested. This study reports quantitative and morphological characterization of antigen delivery from phagosomes into cytoplasm for MHC class I-restricted antigen presentation. Ovalbumin (OVA) was associated with polystyrene particles (PS), biodegradable poly-e-caprolactone particles (PCL), and sheep red blood cells (SRBC), and its delivery into macrophage cytoplasm, via phagocytosis was assessed with a T hybridoma assay for MHC class I-restricted presentation of OVA-derived peptides. Although direct introduction of antigen into cytoplasm by scrape-loading produced the most efficient presentation, comparable signals could be obtained after phagocytosis of PCL or PS. Phagocytosis of OVA-loaded SRBC, and OVA internalized by pinocytosis, did not deliver efficiently. MHC class I-restricted presentation of phagosome-derived OVA required cytoplasmic processing, as it was inhibited by proteasome inhibitors and brefeldin A. Morphological studies showed that biotinylated OVA originating in PCL phagosomes could be delivered into the cytoplasm of 90% of the macrophages. These results indicate that phagocytosis per se is not sufficient to deliver antigen into cytoplasm, but that phagocytosis of solid, synthetic polymeric particles delivers antigen efficiently into cytoplasm for MHC class I processing.

Animals↗
PubMed1997

Cellular retention of liposome-delivered anionic compounds modulated by a probenecid-sensitive anion transporter.

PURPOSE: Drug carriers such as liposomes may enhance the intracellular delivery of therapeutic agents for infectious or neoplastic diseases. However, the mechanisms affecting cellular retention of liposome contents are understood poorly. We tested the hypothesis that retention of anionic compounds may be modulated by a nonspecific probenecid-sensitive anion transport mechanism, and that liposome composition may determine the impact of such transporters on drug retention by cells. METHODS: The fluorescent anionic dye hydroxy-pyrene-[1,3,6]-trisulfonate (HPTS) was transferred to the cytoplasm of cultured CV-1 or J774 cells by direct needle-microinjection or by ATP-induced permeabilization of the-plasma membrane, respectively, to investigate whether the cells have anion transport mechanisms capable of extruding HPTS from the cytoplasm. Cellular retention of dye was monitored in the presence and absence of the anion transport inhibitors probenecid or sulfinpyrazone. Liposomes containing HPTS were co-labeled with tetramethylrhodamine-labeled phosphatidylethanolamine (Rho-PE) as a marker of liposome membrane fate, and uptake was investigated using J774 cells. RESULTS: Needle-injected HPTS underwent both sequestration in early endocytic vesicles and rapid extrusion into the extracellular medium. Probenecid or sulfinpyrazone reduced the extrusion of HPTS. Thus HPTS is a substrate for a probenecid-sensitive anion transporter in J774 and CV1 cells. After delivery via fluid liposomes composed of phosphatidylglycerol:phosphatidylcholine:cholesterol (3:7:5 mole ratio) and co-labeled with Rho-PE, cell-associated HPTS declined more rapidly than did Rho-PE. Exposure of cells to 5 mM probenecid doubled the quantity of HPTS retained by cells, without changing the retention of the Rho-PE membrane marker. In contrast, the effect of probenecid was negligible when gel-phase liposomes of distearoylphosphatidylglycerol:cholesterol (10:5 mole ratio) were used. CONCLUSIONS: Probenecid-sensitive nonspecific anion transporters can mediate the extrusion of model anions delivered via liposomes. However, liposome composition modulates the amount of material subject to extrusion from cells, possibly by altering the endocytic compartment in which liposomes release their contents.

Animals↗
PubMed1996

Hypothermia-induced changes of afferent sensory transmission to the SI cortex of rats and hamsters.

The effects of acute lowering of body temperature on afferent sensory transmission to the primary somatosensory cortex were determined quantitatively in anaesthetized rats and hamsters. Rats showed no change in afferent sensory transmission until 27 degrees C, but dramatic suppression between 26 degrees C and 22 degrees C, reaching 100% inhibition at 21 degrees C. Hamsters exhibited gradual suppression of sensory transmission from 34 degrees C to 18 degrees C, reaching 95% inhibition at 18 degrees C. Differential effects were also observed during rewarming up to 37 degrees C. Response latencies were also differentially affected during hypothermia in rats and hamsters. These results suggest the presence of inherently different neural mechanisms to process somatosensory information during transient lowering of body temperature between hibernators and non-hibernators.

Animals↗
PubMed1996

Delivery of macromolecules into cytosol using liposomes containing hemolysin from Listeria monocytogenes.

The cytosolic space of cells is an important but relatively inaccessible target for the delivery of therapeutic macromolecules. Here we describe the efficient delivery of macromolecules into the cytosolic space of macrophages from liposomes that contain listeriolysin O (LLO), the hemolytic protein of Listeria monocytogenes that normally mediates bacterial passage from phagosomes into cytosol. LLO was purified and encapsulated inside pH-sensitive liposomes, along with other molecules to be delivered. When internalized by bone marrow-derived macrophages, these liposomes rapidly released encapsulated fluorescent dye, first into endosomes and then into the cytosol, without measurably harming the cells. Furthermore, these liposomes efficiently delivered encapsulated ovalbumin to the cytosolic pathway of antigen processing and presentation, as measured by the major histocompatibility complex (MHC) class I-restricted presentation of peptides derived from ovalbumin. Delivery was significantly better than that obtained by other currently available liposome formulations. LLO-containing liposomes should therefore provide an efficient vehicle for delivery of antigens or therapeutic molecules in vivo.

Animals↗
PubMed1996

Different fates of phagocytosed particles after delivery into macrophage lysosomes.

Phagocytosis in macrophages is often studied using inert polymer microspheres. An implicit assumption in these studies is that such particles contain little or no specific information in their structure that affects their intracellular fate. We tested that assumption by examining macrophage phagosomes containing different kinds of particles and found that although all particles progressed directly to lysosomes, their subsequent fates varied. Within 15 min of phagocytosis, >90% of phagosomes containing opsonized sheep erythrocytes, poly-e-caprolactone microspheres, polystyrene microspheres (PS), or polyethylene glycol-conjugated PS merged with the lysosomal compartment. After that point, however, the characteristics of phagolysosomes changed in several ways that indicated differing degrees of continued interaction with the lysosomal compartment. Sheep erythrocyte phagolysosomes merged together and degraded their contents quickly, poly-e-caprolactone phagolysosomes showed intermediate levels of interaction, and PS phagolysosomes became isolated within the cytoplasm. PS were relatively inaccessible to an endocytic tracer, Texas red dextran, added after phagocytosis. Moreover, immunofluorescent staining for the lysosomal protease cathepsin L decreased in PS phagolysosomes to 23% by 4 h after phagocytosis, indicating degradation of the enzyme without replacement. Finally, PS surface labeled with fluorescein-labeled albumin showed a markedly reduced rate of protein degradation in phagolysosomes, when compared to rates measured for proteins in or on other particles. Thus, particle chemistry affected both the degree of postlysosomal interactions with other organelles and, consequently, the intracellular half-life of particle-associated proteins. Such properties may affect the ability of particles to deliver macromolecules into the major histocompatibility complex class I and II antigen presentation pathways.

Animals↗
PubMed1996

Intracellular fate of Mycobacterium avium: use of dual-label spectrofluorometry to investigate the influence of bacterial viability and opsonization on phagosomal pH and phagosome-lysosome interaction.

Mycobacterium avium is a facultative intracellular pathogen that can survive and replicate within macrophages. We tested the hypotheses that survival mechanisms may include alteration of phagosomal pH or inhibition of phagosome-lysosome fusion. M. avium was surface labeled with N-hydroxysuccinimidyl esters of carboxyfluorescein (CF) and rhodamine (Rho) to enable measurement of the pH of individual M. avium-containing phagosomes and the interactions of bacterium-containing phagosomes with labeled secondary lysosomes. CF fluorescence is pH sensitive, whereas Rho is pH insensitive; pH can be calculated from their fluorescence ratios. Surface labeling of M. avium did not affect viability in broth cultures or within J774, a murine macrophage-like cell line. By fluorescence spectroscopy, live M. avium was exposed to an environmental pH of approximately 5.7 at 6 h after phagocytosis, whereas similarly labeled Salmonella typhimurium, zymosan A, or heat-killed M. avium encountered an environmental pH of < 5.0. Video fluorescence and laser scanning confocal microscopy gave consistent pH results and demonstrated the heterogeneity of intracellular fate early in infection. pH became more homogeneous 6 h after infection. M. avium cells were coated with immunoglobulin G (IgG) or opsonized to investigate whether phagocytosis by the corresponding receptors would alter intracellular fate. Opsonized, unopsonized, and IgG-coated M. avium cells entered compartments of similar pH. Finally, the spatial distribution of intracellular bacteria and secondary lysosomes was compared. Only 18% of live fluorescent M. avium cells colocalized with fluorescent lysosomes, while 98% of heat-killed bacteria colocalized. Thus, both inhibition of phagosome-lysosome fusion and alteration of phagosomal pH may contribute to the intracellular survival of M. avium.

Animals↗
PubMed1996

Rapid and complete fusion of macrophage lysosomes with phagosomes containing Salmonella typhimurium.

The virulence of Salmonella typhimurium for mice results, in part, from its ability to survive after phagocytosis by macrophages. Although it is generally agreed that intracellular bacteria persist in membrane-bound phagosomes, there remains some question as to whether these phagosomes fuse with macrophage lysosomes. This report describes the maturation of phagosomes containing S. typhimurium inside mouse bone marrow-derived macrophages. Macrophages were infected briefly and incubated for various intervals; then they were examined by fluorescence microscopy for colocalization of bacteria with lysosomal markers. These markers included LAMP-1, cathepsin L, and fluorescent proteins or dextrans preloaded into lysosomes by endocytosis. By all measures, phagosomes containing S. typhimurium merged completely with the lysosomal compartment within 20 min of phagocytosis. The rate of phagosome-lysosome fusion was similar to the rate for phagocytosed latex beads. Phagolysosomes remained accessible to fluid-phase probes and contained lysosomal markers for many hours. Moreover, a large percentage of the wild-type bacteria that were viable 20 min after infection survived longer incubations inside macrophages, indicating that the survivors were not a minor subpopulation that avoided phagosome-lysosome fusion. Therefore, we conclude that S. typhimurium survives within the lysosomal compartments of macrophages.

Animals↗
PubMed1995

Formulation and efficacy of liposome-encapsulated antibiotics for therapy of intracellular Mycobacterium avium infection.

Mycobacterium avium is an intracellular pathogen that can invade and multiply within macrophages of the reticuloendothelial system. Current therapy is not highly effective. Particulate drug carriers that are targeted to the reticuloendothelial system may provide a means to deliver antibiotics more efficiently to M. avium-infected cells. We investigated the formulation of the antibiotics ciprofloxacin and azithromycin in liposomes and tested their antibacterial activities in vitro against M. avium residing within J774, a murine macrophage-like cell line. A conventional passive-entrapment method yielded an encapsulation efficiency of 9% for ciprofloxacin and because of aggregation mediated by the cationic drug, was useful only with liposomes containing < or = 50 mol% negatively charged phospholipid. In contrast, ciprofloxacin was encapsulated with > 90% efficiency, regardless of the content of negatively charged lipids, by a remote-loading technique that utilized both pH and potential gradients to drive drug into preformed liposomes. Both the cellular accumulation and the antimycobacterial activity of ciprofloxacin increased in proportion to the liposome negative charge; the maximal enhancement of potency was 43-fold in liposomes of distearoylphosphatidylglycerol-cholesterol (DSPG-Chol) (10:5). Azithromycin liposomes were prepared as a freeze-dried preparation to avoid chemical instability during storage, and drug could be incorporated at 33 mol% (with respect to phospholipid). Azithromycin also showed enhanced antimycobacterial effect in liposomes, and the potency increased in parallel to the moles percent of negatively charged lipids; azithromycin in DSPG-Chol (10:5) liposomes inhibited intracellular M. avium growth 41-fold more effectively than did free azithromycin. Thus, ciprofloxacin or azithromycin encapsulated in stable liposomes having substantial negative surface charge is superior to nonencapsulated drug in inhibition of M.avium growth within cultured macrophages and may provide more effective therapy of M.avium infections.

Animals↗
PubMed1987

Actinoidin A2, a novel glycopeptide: production, preparative HPLC separation and characterization.

An unidentified Nocardia sp. (SK&F-AAJ-193) was isolated and found to produce actinoidin A and a novel analog which we have named actinoidin A2. This new glycopeptide antibiotic differs from actinoidin A by the presence of rhamnose instead of acosamine. This analog was isolated using Dianion HP-20 resin followed by a specific glycopeptide affinity column (Affigel-10-D-Ala-D-Ala). The purification was accomplished using preparative ion-pairing chromatography. Actinoidin A2 is active against Staphylococcus aureus and coagulase-negative Staphylococci although it is less potent than actinoidin A.

Animals↗
PubMed1986

Kibdelins, novel glycopeptide antibiotics. I. Discovery, production, and biological evaluation.

A new subspecies of Kibdelosporangium aridum subsp. largum (SK&F AAD-609), was isolated and shown to produce novel glycopeptides related to aridicins, but containing a homologous series of glycolipids based on N-acylglucosamine. These compounds showed improvements over the aridicins in in vitro activity and were effective in mouse protection studies against a range of Gram-positive bacteria, including methicillin resistant staphylococci. Pharmacokinetic studies indicated that they have high serum concentrations and long-acting potential. The kibdelin complex modified rumen metabolism in a manner favorable for growth promotion.

Actinomycetales↗