Biomedical subjects

N Oku

Publications and source records attributed to N Oku.

At least 19 recordsLinked to original sources

PubMed2000

Relationship between brain zinc and transient learning impairment of adult rats fed zinc-deficient diet.

The relationship between brain zinc and learning behavior was studied based on the data of 65Zn localization in the hippocampal formation. Learning behavior, tested by passive avoidance performance, of 6-week-old rats improved significantly compared to that of 4-week-old rats and it was maintained at 20 weeks of age. When 8-week-old rats were fed zinc-deficient diet for 4 weeks, the learning behavior was significantly impaired. However, it was recovered to almost normal level by feeding with control (zinc-adequate) diet for 5 weeks. These results demonstrate that a proper zinc supply to the brain is necessary for improvement and maintenance of learning ability. Although an appreciable decrease in brain zinc was not observed in the rats fed zinc-deficient diet for 4 weeks, significant decrease of hippocampal zinc was observed in rats fed zinc-deficient diet for 12 weeks. Moreover, synaptosomal zinc in the hippocampal formation and cerebral cortex was significantly decreased by the 12 weeks of zinc deprivation. These results suggest that the decrease of vesicular zinc in the hippocampal formation and cerebral cortex is involved in the transient learning impairment of adults rats.

Age Factors↗

PubMed2000

Functional brain areas used for the lifting of objects using a precision grip: a PET study.

Positron emission tomography (PET) was performed in 10 normal volunteers to investigate regional cortical and subcortical activation induced by the lifting of an object repetitively using a precision grip between the index finger and thumb. Data were obtained for three object weights (4, 200 and 600 g) and a resting condition. Grip and lift forces on a similar object and the activity of selected muscles in the hand, arm and shoulder were also recorded in separate lifting trials. A comparison between all movement conditions and the resting condition revealed significant activation of the primary motor (M1), primary sensory (S1), dorso-caudal premotor (PM), caudal supplementary motor (SMA) and cingulate motor (CMA) cortices contralateral to the hand used. On the ipsilateral side, activation of the M1, caudal SMA and inferior parietal cortex (BA 40) was also found. In the subcortical areas, the bilateral hemispheres and right vermis of the cerebellum, left basal ganglia and thalamus were activated. Behavioral adaptation to a heavier object weight was revealed in a nearly proportional increase of both grip and lift forces, prolonged force application period and a higher level of hand and arm muscle activities. An increase in the rCBF associated with these changes was noted in several cortical and subcortical areas. However, consistent object weight-dependent activation was observed only in the M1/S1 contralateral to the hand used.

Adult↗

PubMed2000

Possible role of immune surveillance at the initial phase of metastasis produced by B16BL6 melanoma cells.

The relationship among the real-time trafficking of lung metastatic B16BL6 cells, metastatic potential, and the injected number of the cells was examined, since the smaller the number of tumor cells injected, the more clearly the immune defense may be observed. When 1x10(6) or 1x10(5) B16BL6 cells were injected into mice via the tail vein, both numbers of cells accumulated in the lung at a similar rate: there was an approximately 10-fold difference in the number of accumulated cells between the two doses. Elimination from the lung was not dependent on the cell number but on the proportion of accumulated cells. However, the injection of 1x10(4) cells resulted in lung accumulation less than one-tenth of that obtained with 1x10(5) cell injection. Metastasis was observed when 1x10(5) or 1x10(6) B16BL6 cells were injected, but not after injection of 1x10(4) cells. To clarify the roles of the immune defense system at the initial phase of metastasis, we challenged macrophage-depleted mice with 1x10(4) tumor cells. Treatment of mice with 2-chloroadenosine prior to the tumor cell challenge cancelled the suppression of not only metastasis but also the lung accumulation. Furthermore, the administration of 2-chloroadenosine following the tumor cell challenge had little effect on the metastatic potential. These results suggest that the immune surveillance whose action was obvious at the low dose of challenged tumor cells functions strongly at the initial phase but not at the advanced stages of the metastatic process, and that macrophages play an important role in the suppression of metastasis.

2-Chloroadenosine↗

PubMed2000

Suppression of GD1alpha ganglioside-mediated tumor metastasis by liposomalized WHW-peptide.

GD1alpha ganglioside-replica peptides were recently isolated from a phage-displayed random pentadecapeptide library by assaying for inhibition of adhesion of RAW117-H10 lymphosarcoma cells to hepatic sinusoidal microvessel endothelial (HSE) cells. We show here that the Trp-His-Trp (WHW) peptide was identified as a minimal sequence of the GD1alpha-replica peptide WHWRHRIPLQLAAGR. The addition of WHW peptide-attached liposomes displayed efficient inhibition of liver metastasis of RAW117-H10 cells as well as of GD1alpha-mediated adhesion of RAW117-H10 cells to HSE cells in vitro. These results suggest that engineered liposomes for peptide delivery are applicable to treatment for metastasis.

Amino Acid Sequence↗

PubMed2000

The neural basis of perceptual and conceptual word priming--a PET study.

Positron emission tomography scans were obtained in 13 normal subjects during perceptual and conceptual word priming tasks with the aim to investigate the neural system specific to the two priming conditions. In the prescan phase, subjects were primed perceptually or conceptually with two separate procedures, while in the scan phase, they performed the same stem completion task. Therefore we could compare the results of the two priming tasks in a direct manner. A fixation control task and a baseline task (completion of stems that did not correspond to previously seen words) were also given. A specific blood flow decrease was found in the left inferior temporal cortex in the perceptual word priming condition and in the left superior temporal / inferior parietal cortex in the conceptual word priming condition. Each blood flow change may reflect transient changes in the cortical areas subserving the processing of the perceptual and conceptual components of word priming.

Adult↗

PubMed2000

New isomalabaricane triterpenes from the marine sponge Stelletta globostellata that induce morphological changes in rat fibroblasts.

Three new isomalabaricane triterpenes, 29-hydroxystelliferin D (2), 3-epi-29-hydroxystelliferin E (3), and 3-epi-29-hydroxystelliferin A (4), were isolated from the marine sponge Stelletta globostellata. Their structures, including absolute stereochemistry, were determined on the basis of spectral data and chemical methods. Rat fibroblasts treated with 0.2 microM of 2-4 exhibited unusual morphological characteristics, followed by death in 5 days.

Acetylation↗

PubMed2000

Magnetic resonance lymphography of profundus lymph nodes with liposomal gadolinium-diethylenetriamine pentaacetic acid.

Lymphography, especially imaging of profundus lymph nodes, is a useful tool for diagnosis of cancer metastases in lymph nodes. However, positive enhancement agents for magnetic resonance lymphography (MRL) have not been available, since the positive imaging agents so far introduced are low-molecular-weight materials that are not trapped in lymph nodes. For the purpose of improved positive enhanced MRL, we employed liposomes as carriers of a positive enhancer, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Magnetic resonance (MR) imaging was performed after subcutaneous injection of Gd-liposomes into the hind feet of rabbits which had reactive enlarged retroperitoneal lymph nodes. As a result, not only popliteal but also profundus retroperitoneal lymph nodes were positively enhanced by Gd-liposomes, especially after 20 min massage of the injected sites. Gd-Liposomes containing dipalmitoylphosphatidylglycerol were more effective than Gd-liposomes containing palmityl-D-glucuronide, a type of long-circulating liposomes, suggesting that liposomal accumulation in lymph node is, at least partly, mediated by the trapping of liposomes by macrophages. These data show that liposomes modified with Gd-DTPA are effective for positive enhancement of both regional and profundus lymph nodes in MR lymphography.

Animals↗

PubMed1999

Release of zinc from the brain of El (epilepsy) mice during seizure induction.

Brain distribution after i.v. injection of 65ZnCl2 into El mice, an animal model of genetically determined epilepsy, was studied by autoradiography to study the utilization of zinc in the brain. The distribution of 65Zn in the brain of El mice 6 days after injection was almost the same as that of ddY (normal) mice, suggesting that the uptake of zinc by the brain of El mice is normal. To study the movement of zinc in the brain in the course of seizure induction, the concentrations of 65Zn in the brain of seizure-afflicted and untreated control El mice were compared 20 days after 65Zn injection. The concentration of 65Zn in the brain of seized El mice was overall lower than that of control El mice; the concentration of 65Zn was decreased notably in the piriform cortex and amygdaloid nuclei complex during convulsion. These results suggest that the release of zinc from the El mouse brain is enhanced during convulsion. The decrease in actively functioning zinc in the brain may be associated with the increase in susceptibility to seizure in the El mouse.

Animals↗

PubMed1999

109Cd transport in rat brain.

The brain distribution of 109CdCl2 following administration into either the tail vein, the lateral ventricle or the olfactory bulb was studied to clarify permeability of the brain barrier system to cadmium (Cd) and Cd movement in the cerebrospinal fluid (CSF) and the brain extracellular fluid. One hour after intravenous (i.v.) injection, 109Cd was largely concentrated in the choroid plexus, and 109Cd concentration in the major part of the brain parenchyma, except for the circumventricular organs such as the pineal gland and the regions around them, was low. Six days after i.v. injection, 109Cd concentration in the choroid plexus was still high, and 109Cd was also detected highly in the pineal gland and small part around the median eminence. 109Cd concentration in the major part of the brain parenchyma was decreased in parallel with that in the blood. In the case of injection of 109CdCl2 into the lateral ventricle, a large portion of 109Cd was detected in the ventricular system 6 days after injection, and 109Cd concentration in the major part of the brain parenchyma was less than the detection limit. These results suggest that Cd cannot easily get into the brain and is blocked not only by the blood- brain and the blood-CSF barriers, but also by the ependymal and pial surfaces. In the case of injection of 109CdCl2 into the olfactory bulb, a large portion of 109Cd was detected in the injected area 24 h after injection, and, the next 24 h later, 109Cd distribution in the brain was not changed appreciably. These results suggest that Cd cannot easily move in the brain extracelular space, and is taken up into the brain parenchyma.

Animals↗

PubMed1999

Application of surface-coated liposomes for oral delivery of peptide: effects of coating the liposome's surface on the GI transit of insulin.

We prepared two kinds of surface-coated liposomes and investigated their potencies as oral dosage forms for peptide drugs by focusing on their effects on the gastrointestinal (GI) transit of drugs. The surface of the liposomes was coated with poly(ethylene glycol) 2000 (PEG-Lip) or the sugar chain of mucin (Mucin-Lip). As a model peptide drug, insulin was encapsulated in these liposomes. Coating the surface with poly(ethylene glycol) was found to reduce the transit rate of liposomes in the small intestine after oral administration to rats in vivo. Mucin-Lip was retained in the stomach longer than PEG-Lip or uncoated liposomes. The effect of surface coating on the intestinal transit of liposomes was determined by means of in situ single pass perfusion in the rat small intestine. Statistical moment analysis was applied to the outflow pattern of both liposomes and encapsulated insulin. The mean transit time (MTT) and deviation of transit time (DTT) in the intestinal tract were calculated. The MTT of PEG-Lip was much longer than those of uncoated liposomes and Mucin-Lip and was significantly shortened after removal of the intestinal mucous layer. These results indicated that PEG-Lip interacts strongly with the intestinal mucous layer, leading to its slow transit in the intestine. In contrast, coating the liposome's surface with mucin did not affect either the MTT or DTT of liposomes in the intestine. This result is in accordance with the in vivo observation that Mucin-Lip was highly retained in the stomach, but not in any region of the small intestine in vivo. Both the MTT and DTT values of insulin encapsulated in PEG-Lip and Mucin-Lip were almost the same as those of liposomes themselves, suggesting that surface-coated liposomes retained insulin in the intestinal tract. However, MTT and DTT of insulin were significantly shorter than those of uncoated liposomes because these liposomes degraded and released significant amounts of insulin during single pass perfusion. The ability of surface-coated liposomes, especially of PEG-Lip, to interact with the mucus layer and slow the transit rate in the GI tract is considered desirable for oral delivery of peptide drugs. Modification of the liposomal surface with appropriate materials, therefore, should be an effective method by which to achieve the oral delivery of peptide drugs.

Animals↗

PubMed1999

Perception and conception: separate memory systems in the medial temporal lobe.

The purpose of the present study was to investigate, by using positron emission tomography, whether the functionally different types of information are subserved by different memory systems in human medial temporal lobe structures. Before explicit retrieval tests during scans, subjects studied words in perceptually and conceptually processed manners separately. It was found that different parts of the medial temporal lobe structures were involved in each of the different conditions. These results indicated that perceptually and conceptually processed types of information were subserved by at least two partially segregated memory systems in human medial temporal lobe structures.

Adult↗

PubMed1998

GD1alpha-replica peptides functionally mimic GD1alpha, an adhesion molecule of metastatic tumor cells, and suppress the tumor metastasis.

A novel peptide technology to produce mimicking peptides of carbohydrate moiety (which we propose to name glyco-replica peptides) is a useful tool to elucidate the functions of glycoconjugate. Carbohydrate moiety of ganglioside GD1alpha functions as a molecule involved in the adhesion between murine highly metastatic lymphoma RAW117-H10 cells and hepatic sinusoidal endothelial (HSE) cells. To prepare peptides which mimic the carbohydrate structure of GD1alpha, phage clones expressing peptides which bound to a monoclonal antibody against GD1alpha (KA17) were isolated from a phage-displayed random peptide library. Four phage clones having affinity to the monoclonal antibody KA17 were isolated, and these clones showed inhibitory effect on the binding of KA17 to GD1alpha. The amino acid sequences of the displayed pentadecamers were determined, and one of the phages displaying sequence WHWRHRIPLQLAAGR bound to HSE cells directly and showed the highest inhibitory effect on the adhesion between RAW117-H10 cells and HSE cells. The synthesized peptides having the same sequences to the displayed 15mers in the four isolated phage clones also showed the inhibitory effect on the adhesion of RAW117-H10 cells to HSE cells, and, again, the WHWRHRIPLQLAAGR peptide showed the highest inhibitory effect. Furthermore, intravenous injection of the peptide brought almost complete inhibition of the metastasis of RAW117-H10 cells to lung and spleen, and about 50% inhibition of the liver metastasis. These results indicate that GD1alpha plays an important role for metastasis of RAW117-H10 cells, and the peptides obtained by the present procedure are able to mimic the functional role of the glycoconjugate.

Amino Acid Sequence↗

PubMed1998

How platelet aggregation affects B16BL6 melanoma cell trafficking.

In blood-borne metastasis, intravasated metastatic tumor cells are thought to localize at the target site via a series of processes involving platelet aggregation, adhesion to endothelium, and invasion through the basal membrane. In the present study, we examined how platelet aggregation contributes to the trafficking of metastatic tumor cells in vivo by use of an inhibitor of platelet aggregation. Highly invasive B16BL6 melanoma cells were labeled with [2-18F]2-fluoro-2-deoxy-D-glucose and injected into mice to determine cell trafficking non-invasively by positron emission tomography. Both platelet aggregation inhibitor cyclo(RSarDPhg), which could not inhibit metastasis, and metastatic inhibitor cyclo(GRGDSPA) suppressed the accumulation of B16BL6 cells in the lung by about 12%, suggesting that platelet aggregation partly affects cell trafficking but not to a great extent, and that platelet aggregation is not the essential step for B16BL6 cell arrest in targets.

Animals↗

PubMed1998

Cyclotheonamides E2 and E3, new potent serine protease inhibitors from the marine sponge of the genus Theonella.

Two new potent serine protease inhibitors, cyclotheonamides E2 (3) and E3 (4), have been isolated from a marine sponge of the genus Theonella. Their structures were determined by interpretation of spectral data and chemical degradation studies. They are closely related to the previously reported cyclotheonamide E, from which they differ in the N-acyl group of the alanyl side chain. Cyclotheonamides E, E2, and E3 were more active against thrombin than against trypsin.

Animals↗

PubMed1998

Role of sialylglycoconjugate(s) in the initial phase of metastasis of liver-metastatic RAW117 lymphoma cells.

To elucidate the early events of blood-borne metastasis under actual blood flow, real-time trafficking of RAW117 large cell lymphoma cells, namely parental RAW117-P and liver-metastatic RAW117-H10 cells, was investigated using positron emission tomography (PET). Both types of cells accumulated in the liver immediately after injection via the portal vein, and were eliminated from the liver time-dependently. The elimination rate of RAW117-H10 cells, however, was slower than that of RAW117-P cells, suggesting that RAW117-H10 cells interact more strongly with hepatic sinusoidal endothelium than the parental cells. This result correlated with the metastatic potential of these cells: RAW117-H10 cells metastasized in the liver to a greater extent than RAW117-P cells after injection via this route. To investigate the role of sialylglycoconjugates in the interaction of RAW117-H10 cells with the hepatic endothelium after injection via the portal vein, the trafficking of RAW117-H10 cells was examined after the cells had been treated with sialidase. The elimination rate of RAW117-H10 cells from liver was observed to be greatly accelerated by sialidase treatment. To elucidate what kind of sialylglycoconjugates is related to this phenomenon, we analyzed the distribution of sialyl Lewis A and sialyl Lewis X antigens of both sublines of RAW117 by using flow cytometry. RAW117-H10 cells were found to express a much higher level of sialyl Lewis A than RAW117-P cells, whereas the amount of sialyl Lewis X did not differ significantly. These findings suggest that some sialylglycoconjugates, perhaps sialyl Lewis A in particular, play an important role in the initial interaction of RAW117-H10 cells with the hepatic endothelium, leading to metastasis.

Animals↗

PubMed1998

Beta-thujaplicin zinc chelate induces apoptosis in mouse high metastatic melanoma B16BL6 cells.

The cytotoxic effects of beta-thujaplicin and five kinds of metal chelates were examined on mouse melanoma B16BL6 cells by cell viability and lactate dehydrogenase (LDH) release assay. Beta-thujaplicin-zinc chelate and beta-thujaplicin-copper chelate had higher cytotoxic effects than beta-thujaplicin, and the 50% effective doses (ED50) of these metal chelates were 12.5 and 25 microM, respectively. In addition, the zinc chelate induced DNA ladder formation in B16BL6 cells, as shown by the DNA fragmentation assay, suggesting that cell death induced by the zinc chelate is apoptosis. The zinc chelate also had a cytotoxic effect and induced DNA fragmentation on other tumor cell lines: HeLa, Meth A, and B16F1 cells, but not on normal human diploid fibroblasts FS-4. These results suggest that beta-thujaplicin-zinc chelate induces apoptotic cell death in various tumor cell lines and is a potent antitumor agent for tumor cells including malignant melanomas.

Animals↗

PubMed1998

Antitumor activity of 5'-O-dipalmitoylphosphatidyl 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine is enhanced by long-circulating liposomalization.

We previously synthesized the 5'-O-diacylphosphatidyl derivative of 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC), a novel antitumor nucleoside, and observed it to have a high antitumor activity. Since this compound is readily incorporated into liposomal membranes, we liposomalized the compound using a formulation for conventional and long-circulating liposomes, and investigated the antitumor activity of liposomal 5'-O-dipalmitoylphosphatidyl CNDAC (DPP-CNDAC). Long-circulating liposomes composed of DPP-CNDAC, dipalmitoylphosphatidylcholine, cholesterol and palmityl-D-glucuronide (PGlcUA) (2:2:2:1 as a molar ratio), as well as liposomes containing dipalmitoylphosphatidylglycerol (DPPG) instead of palmityl-D-glucuronide and those composed of only DPP-CNDAC, were injected intravenously into Meth A sarcoma-bearing mice. DPP-CNDAC showed suppression of tumor growth, whereas CNDAC did not at the same concentration, suggesting that 5'-phosphatidylation is useful to enhance therapeutic efficacy. Furthermore, liposomal DPP-CNDAC reduced the acute toxicity, and liposomes containing PGlcUA showed more enhanced activities of reducing tumor growth and increasing the lifetime of the mice than liposomes containing DPPG. To obtain a higher therapeutic efficacy, we injected long-circulating liposomal DPP-CNDAC 5 times. The tumor growth was suppressed to 13.2% (86.8% inhibition), and the survival time of the tumor-bearing mice increased to 128.5% with one completely cured mouse out of five. Next, the effect of DPP-CNDAC incorporation on the in vivo behavior of PGlcUA and DPPG liposomes was examined by a non-invasive method using positron emission tomography (PET). Liposomes were labeled with [2-(18)F]-2-fluoro-2-deoxy-D-glucose, and administered to tumor-bearing mice. PET images and time-activity curves indicated that DPP-CNDAC/PGlcUA-liposomes tended to accumulate in tumor tissues a little bit more than DPP-CNDAC/DPPG-liposomes, although the difference between the two kinds of liposomal distribution was not as marked as between PGlcUA and DPPG liposomes, suggesting that DPP-CNDAC incorporation partly affected the liposomal behavior in vivo but that the long-circulating character of PGlcUA-liposomes might not be fully abolished. Thus, the enhanced therapeutic efficacy of long circulating liposomalized DPP-CNDAC observed here may be due to passive targeting of DPP-CNDAC to the tumor tissue, making this formulation of DPP-CNDAC useful for cancer chemotherapy.

Animals↗

PubMed1998

A new interpretation of salicylic acid transport across the lipid bilayer: implications of pH-dependent but not carrier-mediated absorption from the gastrointestinal tract.

Transport of several monocarboxylic acids across the lipid bilayer was examined in liposomes consisting of egg yolk phosphatidylcholine and cholesterol. In the presence of inward proton gradient, salicylic acid (SA) was taken up rapidly by liposomes showing overshoot, saturation and competitive inhibition phenomena. These carrier-mediated like profiles of SA uptake can be explained by assuming a very high permeability through the liposomal membrane of protonated SA. Protonated SA in the extraliposomal solution (pH 5.8) was taken up by liposomes rapidly, followed by a redissociation to anion according to the intraliposomal pH (pH 7.5). The concentration gradient of protonated SA across the liposomal membrane is maintained until the intraliposomal pH decreased to the extraliposomal level, which facilitates the uptake of SA into liposomes. The permeability of the lipid bilayer to several compounds was estimated from the inhibitory effects of those compounds on SA uptake by liposomes. Good linear relationships were observed between their inhibitory effects on the liposomal uptake of SA and the permeability of the intestinal membrane to them determined both in vivo and in vitro. These results clearly indicate that the carrier-independent transport mechanism of monocarboxylic acids observed in liposomes significantly contributes to their absorption from the intestinal tract under physiological conditions.

Animals↗