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Biomedical subjects

J Dai

Publications and source records attributed to J Dai.

At least 181 records · Page 10Linked to original sources
PubMed1995

Axon membrane flows from the growth cone to the cell body.

During the growth of axons, the surface area of the neuron increases dramatically. Membrane addition as well as exchange could contribute to rapid membrane dynamics or flow. Using diffusing latex beads to monitor membrane flow, we find that axonal membrane flows rapidly (7 microns/min) from growth cone to cell body during axon growth and that flow is inhibited by brefeldin A. To power this flow, there is a membrane lesion gradient from growth cone to cell body that could draw the membrane over the axon at that rate. Further, when an artificial flow is induced to the center of the axon by use of laser tweezers, the primary source of the membrane is from the growth cone. We suggest that during neuron growth, there is excess membrane added at the growth cone in chick dorsal ganglia (DRGs) that undergoes edcocytosis at the cell body, thereby creating a flow that can rapidly alter the content of the axon membrane.

Animals↗
PubMed1995

Plasma clozapine levels and the treatment of L-DOPA-induced psychosis in Parkinson's disease. A high potency effect of clozapine.

The purpose of this study was to determine the plasma level of clozapine and its metabolite, N-desmethylclozapine, in Parkinson's disease patients with L-DOPA-induced psychosis responsive to clozapine. The psychotic symptoms of the three patients studied responded to low doses of clozapine with plasma levels of clozapine between 4.5 and 16.1 ng/ml and N-desmethylclozapine between 2.6 and 6.1 ng/ml, much below the plasma clozapine levels usually found in clozapine-treated refractory schizophrenia or affective disorders (range 100 to 687 ng/ml). Possible mechanisms that may account for clozapine's antipsychotic action in dopaminomimetic-induced psychosis in Parkinson's disease, including serotonin2A (5-HT2A) and dopamine D4 receptor blockade, at plasma levels that would be ineffective in refractory schizophrenia, are discussed. It is suggested that 5-HT2A receptor blockade is the most likely basis for the effectiveness of clozapine in L-DOPA psychosis.

Aged↗
PubMed1995

Plasma concentrations of excitatory amino acids, serine, glycine, taurine and histidine in major depression.

This study was carried out to investigate plasma levels of excitatory amino acids, such as glutamate and aspartate, and glutamine, serine, glycine, taurine and histidine in major depression. The plasma amino acids were determined by means of HPLC in 22 normal controls and 25 unmedicated patients with major depression. Major depression was characterized by higher plasma taurine levels than normal controls. Significantly lower plasma glycine values and a higher serine/glycine ratio were observed in the depressed group. No significant differences in glutamine, histidine, serine or aspartate levels could be detected between the study groups. By means of linear discriminant analysis, a highly significant separation between major depressed subjects and normal volunteers was found using glycine, glutamate and taurine as discriminatory variables. No significant relationships between any of the amino acids and severity of depression could be found. The results suggest that major depression is accompanied by perturbations in the serine/glycine ratio, excitatory amino acids, such as glutamate, and inhibitory amino acids, such as taurine.

Adult↗
PubMed1995

Involvement of thiol groups in the impairment of cardiac sarcoplasmic reticular phospholipase D activity by oxidants.

Considerable phospholipase D (PLD) activity is localized in myocardial sarcoplasmic reticular (SR) membranes, where it may take part in the regulation of Ca2+ movements. In this study, we examined thiol group dependence as a possible regulatory mechanism for SR PLD. SR membranes isolated from rat heart were exposed to four types of thiol group modifiers, which all induced a decrease in SR PLD activity that was prevented by dithiothreitol. Furthermore, since abnormalities in thiol status and Ca2+ homeostasis are characteristic for the myocardial cell damage induced by oxidative stress, we also studied the effects of oxidants on the SR PLD activity. The enzyme was not affected by xanthine-xanthine oxidase, but was depressed by hydrogen peroxide and by hypochlorous acid. These inhibitory effects were prevented by catalase as well as by methionine and dithiothreitol, respectively. Furthermore, reduced glutathione protected against the hydrogen peroxide-induced depression, whereas oxidized glutathione inhibited SR PLD. The results indicate that SR PLD activity is inhibited by nonradical oxidants, hydrogen peroxide and hypochlorous acid, through reversible modification of associated thiol groups. Thus, the enzyme may be controlled by the glutathione redox status of the cardiac cell.

Animals↗
PubMed1995

Mechanical properties of neuronal growth cone membranes studied by tether formation with laser optical tweezers.

Many cell phenomena involve major morphological changes, particularly in mitosis and the process of cell migration. For cells or neuronal growth cones to migrate, they must extend the leading edge of the plasma membrane as a lamellipodium or filopodium. During extension of filopodia, membrane must move across the surface creating shear and flow. Intracellular biochemical processes driving extension must work against the membrane mechanical properties, but the forces required to extend growth cones have not been measured. In this paper, laser optical tweezers and a nanometer-level analysis system were used to measure the neuronal growth cone membrane mechanical properties through the extension of filopodia-like tethers with IgG-coated beads. Although the probability of a bead attaching to the membrane was constant irrespective of treatment; the probability of forming a tether with a constant force increased dramatically with cytochalasin B or D and dimethylsulfoxide (DMSO). These are treatments that alter the organization of the actin cytoskeleton. The force required to hold a tether at zero velocity (F0) was greater than forces generated by single molecular motors, kinesin and myosin; and F0 decreased with cytochalasin B or D and DMSO in correlation with the changes in the probability of tether formation. The force of the tether on the bead increased linearly with the velocity of tether elongation. From the dependency of tether force on velocity of tether formation, we calculated a parameter related to membrane viscosity, which decreased with cytochalasin B or D, ATP depletion, nocodazole, and DMSO. These results indicate that the actin cytoskeleton affects the membrane mechanical properties, including the force required for membrane extension and the viscoelastic behavior.

Adenosine Triphosphate↗
PubMed1995

Serum low density lipoprotein of alcoholic patients is chemically modified in vivo and induces apolipoprotein E synthesis by macrophages.

This work was carried out to investigate the effect of alcohol drinking on serum LDL. Agarose gel electrophoresis showed that LDL samples from alcoholic patients without serious liver disease were more negatively charged and moved faster toward the cathode than LDL from nondrinking control subjects. Rabbit antibodies raised by using keyhole limpet hemocyanin modified in vitro by 4-hydroxynonenal or by acetaldehyde as immunogens reacted more strongly with patients' LDL than with control LDL, indicating the presence of oxidatively modified epitopes and acetaldehyde adducts in alcoholic patients' LDL. LDL of alcoholic patients has decreased vitamin E contents. The electromobility of LDL decreased after abstinence from alcohol and returned to normal in 2 wk, but this was not accompanied by a significant increase in its vitamin E contents. When incubated with mouse peritoneal macrophages, patients' LDL induced apolipoprotein E secretion by threefold over control LDL with a concomitant increase in cellular cholesterol. Our results thus demonstrate that LDL of alcoholic patients has lower vitamin E content, is chemically modified in vivo, and exhibits altered biological function. These changes in heavy alcoholic drinkers may render LDL more atherogenic and thereby may counter the antiatherosclerosis effects of moderate alcohol consumption.

Adult↗
PubMed1995

Endovascular embolization treatment of cerebral arteriovenous malformations (report of 54 cases).

For further research on endovascular embolization treatment of AVMs, 54 patients with AVMs treated with embolization were observed. It was found that embolization was an effective procedure for the treatment of AVMs. Combined treatment of AVMs with presurgical embolization and direct surgery could reduce the complications resulting from large and high flow AVMs with lone surgical removal.

Adolescent↗
PubMed1995

Integrin-cytoskeletal interactions in neuronal growth cones.

Development of the nervous system requires that neuronal growth cones, in coordination with growing axons, migrate along precise paths defined by specific extracellular matrix cues until they encounter their targets. Laminin promotes growth cone migration through receptors such as the integrins, but the underlying physical mechanism is poorly understood. We have investigated the cytoskeletal associations and surface dynamics of endogenous beta 1 integrins in chick dorsal root ganglion growth cones migrating on laminin. A single-beam optical gradient trap was used to place 0.5-micron-diameter polystyrene beads conjugated with anti-beta 1 integrin monoclonal antibodies at desired locations on the growth cone surface. We found a substantial increase in the stable attachment of these beads, with subsequent slow rearward motion, on the front periphery of the growth cone compared to the base. The surface dynamics of smaller aggregates of integrin were explored by monitoring the temporal and spatial displacements of 40-nm-diameter gold particles coated with anti-beta 1 integrin antibodies. The small particles were transported preferentially to the growth cone periphery by brief directed excursions interspersed with periods of diffusion. In addition, the leading edge of the growth cone was supported to a greater extent by an actin-dependent cytoskeleton that resisted mechanical tether formation. Such a regional differentiation of the growth cone has not been documented previously and has implications for the mechanism of growth cone migration and guidance.

Animals↗
PubMed1994

Preparative separation of naphthyltetrahydroisoquinoline alkaloids from Ancistrocladus korupensis by centrifugal partition chromatography.

Crude extracts of Ancistrocladus korupensis contain a complex mixture of naphthyltetrahydroisoquinoline alkaloids, including the human immunodeficiency virus-inhibitory dimeric alkaloids michellamines A and B and the antimalarial monomeric korupensamines A-D. The efficient separation of michellamines A and B from these extracts has been accomplished by centrifugal partition chromatography. The chromatographic conditions used on a multi-channel cartridge unit (Sanki LLN) have been successfully scaled up with a newly developed, stacked-disk type centrifugal partition chromatography unit (Sanki NMF) for separating larger amounts of alkaloid mixtures with similar resolution. A refined, three-step process (solvent-solvent partitioning, centrifugal partition chromatography and HPLC) has been developed and applied to the scaled-up production of michellamine B for preclinical drug development.

Alkaloids↗
PubMed1994

Purification and characterization of the acid-labile subunit of rat serum insulin-like growth factor binding protein complex.

Circulating insulin-like growth factor (IGF) binding protein-3 (IGFBP-3), when occupied by IGF-I or IGF-II, combines with an acid-labile glycoprotein subunit (ALS) to form a high molecular weight complex. In this study, ALS from rat serum has been purified and its properties investigated. Purification involved ion-exchange chromatography, and affinity chromatography on an IGF-I-IGFBP-3 column, yielding almost 1 mg ALS from 100 ml serum. Amino-terminal sequencing confirmed the prediction from previous complementary DNA analysis but indicated that the protein may circulate in a truncated form. Rat ALS was almost as potent as human ALS in binding to human IGF-I-IGFBP-3 complex (association constant, 2.3 nM-1). A sensitive RIA was developed, with high specificity for rodent ALS. Serum ALS rose from 3 micrograms/ml in 2-day-old rats to more than 40 micrograms/ml at 10 weeks, with no sex difference. GH-deficient rats showed 60-75% lower values than controls. This study shows rat ALS to have similar binding properties, and age and GH dependence, to human ALS. The new RIA will facilitate studies of IGF and IGFBP regulation in the rat.

Aging↗
PubMed1994

Cellular localization and regulation of gene expression for components of the insulin-like growth factor ternary binding protein complex.

Insulin-like growth factors (IGFs) are present in the circulation, largely as part of a high mol wt complex including IGF-binding protein-3 (IGFBP-3) and an acid-labile subunit (ALS). This study used in situ hybridization to investigate the cellular sites of synthesis of these factors in the rat and to evaluate changes in transcript levels during development and after hypophysectomy and GH treatment. IGFBP-3 transcripts are considerably more abundant and widely expressed than ALS at birth, but both are present in liver and kidney. Hepatic IGFBP-3 gene expression increases slightly, whereas ALS increases dramatically in the first few weeks after birth. IGFBP-3 mRNA is concentrated in portal venous and sinusoidal endothelium, but is not detected in hepatocytes, whereas ALS mRNA is diffusely expressed by hepatocytes, but is not detected in nonparenchymal cells. Both transcripts are localized in the renal cortex; however, IGFBP-3 mRNA is concentrated in interstitial cells, whereas ALS is expressed in proximal tubule epithelium. Hypophysectomy results in a 90% reduction in hepatic ALS and an approximately 50% decrease in IGFBP-3 mRNA level. ALS, but not IGFBP-3, transcripts were also reduced in the kidney. GH receptor mRNA is coexpressed with ALS in liver and kidney, suggesting that the effects of GH on ALS gene expression may be direct. In summary, the fact that IGFBP-3 gene expression is far more widespread than that of ALS in both spatial and temporal parameters suggests that IGFBP-3 has a role apart from contribution to the ternary complex. We have also shown that IGFBP-3 and ALS are synthesized by distinct hepatic cell types in an anatomical organization that may serve to ensure efficient formation of the ternary complex in the blood passing through the sinusoids. Finally, the present data suggest that regulation of ALS synthesis may be the primary site of GH regulation of ternary complex formation.

Animals↗
PubMed1994

Regulation of the acid-labile subunit of the insulin-like growth factor complex in cultured rat hepatocytes.

The acid-labile subunit (ALS) is a glycoprotein that forms a ternary complex in serum with insulin-like growth factors and insulin-like growth factor-binding protein-3. This study investigates the regulation of ALS production, measured by RIA, and messenger RNA (mRNA) content, measured by Northern analysis, in primary rat hepatocyte monolayer cultures. Hepatocytes produced ALS at a linear rate over 48 h. Exposure to human GH (30 ng/ml) caused a maximum 2.2-fold stimulation of ALS production compared to that in control cultures, giving a rate of 200 ng/10(6) cells.48 h. ALS mRNA appeared as a predominant 2-kilobase band and increased 4-fold by administration of 30 ng/ml GH. Both dexamethasone and epidermal growth factor (EGF) inhibited ALS production, with maximal effects at 100 nM dexamethasone and 50 ng/ml EGF (both approximately 50% inhibition). ALS mRNA levels measured 24 or 48 h after dexamethasone addition were decreased 75-80% compared to the control value. A similar decrease in ALS mRNA was observed 24 h after EGF addition, but a second addition of EGF at 24 h was required to maintain this decrease for 48 h. This study demonstrates that rat hepatocytes secrete immunoreactive ALS under GH regulation, and that EGF and corticosteroid inhibit ALS production and mRNA levels. The quantitative discrepancies between ALS production rates and mRNA levels suggest that posttranscriptional events may have a role in ALS regulation.

Acids↗
PubMed1994

Regulation in vivo of the acid-labile subunit of the rat serum insulin-like growth factor-binding protein complex.

The acid-labile subunit (ALS) and insulin-like growth factor (IGF)-binding protein-3 are glycoproteins that form a complex carrying about 90% of the circulating IGFs. This study investigates the regulation of ALS expression by Northern hybridization, and serum ALS levels by RIA, in the rat. Northern analysis of ALS messenger RNA (mRNA) from adult rat brain, heart, lung, muscle, spleen, testis or ovary, kidney, and liver showed a liver-specific predominant 2-kilobase transcript. The steady state abundance of rat ALS mRNA was greatly reduced in neonatal and weanling liver compared to adult liver, with an age dependence similar to that of rat serum ALS levels. Fasting for 24 or 48 h decreased serum IGF-I and ALS levels, but not hepatic ALS mRNA. Streptozotocin-diabetic rats, untreated or treated with human GH for 5 days, had significantly decreased serum ALS levels and liver ALS mRNA abundance. Insulin treatment normalized serum ALS without fully restoring ALS mRNA. Dexamethasone, an inhibitor of ALS synthesis by hepatocytes, significantly reduced both serum ALS and hepatic ALS mRNA. The discrepancies between hepatic expression and serum ALS levels in fasting and diabetes point to a complex regulatory mechanism in which events at the translational level or later may be as important as regulation of gene expression or mRNA stability.

Acids↗
PubMed1994

[Propagation of the HTV in primary human embryonic kidney and lung cell culture].

2 strains of Hantaan virus (HTV, 76-118, Hubei-114) have been propagated successfully in cultured primary human embryonic kidney (HEK) and lung (HEL) cells. Cytopathic effect (CPE) was observed in the two kind of cells on day 5 to 7 postinoculation which showed the cell became round and clustered, then detached. The replicating peak of the Hubei-114 in two kinds of cell cultures appeared on the 11th day and another strain on the 14th or 17th day after infection. The ultrastructure changes were observed with EM and IEM, which stained by ICGT before embedding. It was discovered that the mitochondia atrophied and decreased, and inclusion bodies in the cytoplasma of HEK and KEL cells. A large amount of gold granulae were found in the inclusion bodies and the virions were seen occasionally. Contamination with other agents have been ruled out. Our data suggest that the replicating characters of HTV in these cell systems might be possible for the pathogenicity of HFRS for human.

Cells, Cultured↗