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Biomedical subjects

M Li

Publications and source records attributed to M Li.

At least 991 records · Page 55Linked to original sources
PubMed1993

An asynchronous unfolding among molecular different regions of lobster D-glyceraldehyde-3-phosphate dehydrogenase and maltotetraose-forming amylase from an Alcaligenes sp. during guanidine denaturation.

Changes in ultraviolet absorbance and intrinsic protein fluorescence of 1,4-alpha-D-glucan maltotetrahydrolase (EC 3.2.1.60) from an Alcaligenes sp. (Gram-negative bacteria 537.1) and D-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) have been compared with their inactivation during denaturation in guanidinium-Cl solutions. The two enzymes were completely inactivated at GuHCl concentrations less than 0.6 M and this was accompanied by marked absorbance and intrinsic fluorescence changes suggesting exposure of aromatic residues. The changes of the intrinsic fluorescence of the amylase have a relatively constant plateau in emission intensities and maxima at GuHCl concentrations from 0.8-2.0 M, similar to that of muscle GAPDH. The relative activity of the enzyme increased markedly in dilute GuHCl solutions accompanied by very little change of its intrinsic fluorescence at 8 degrees C. The kinetic decrease in emission intensities, excited respectively by 230 nm and 292 nm, was different for the two enzymes. The inactivation was a biphasic process with a fast phase faster than the unfolding rate as measured by fluorescence changes in 0.5 M GuHCl solution. Similar to the inactivation process, changes in intensity of 410 nm NAD fluorescent derivative of GAPDH which is in situ at the active site is also a biphasic process under the same condition. It appears that there may be an unfolding intermediate state of the enzymes and an asynchronous unfolding process among the different regions in the molecules during GuHCl denaturation, this may be due to differences in their flexibility.

Alcaligenes↗
PubMed1993

Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and low-affinity nerve growth factor receptor (LNGFR) mRNA levels in cultured rat Schwann cells; differential time- and dose-dependent regulation by cAMP.

Steady-state mRNA levels for NGF, BDNF, and NT-3, and their receptors, LNGFR, trk, trkB, and trkC, were examined in cultured rat Schwann cells. NGF, BDNF, and LNGFR mRNAs were expressed in control Schwann cells, but NT-3, trk, trkB and trkC mRNAs were not. As previously reported, when Schwann cells were treated with forskolin or 8-bromo-cAMP, NGF mRNA expression was enhanced, while BDNF and LNGFR mRNA levels were suppressed. The optimal concentration of forskolin for NGF mRNA enhancement and BDNF mRNA suppression was similar to that for LNGFR mRNA suppression, which coincided with the optimal concentration for Schwann cells to differentiate. However, the lag-time for forskolin-induces down-regulation of LNGFR mRNA was far greater than that for NGF mRNA increase and BDNF mRNA suppression.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1993

Metabolism of different adipose tissues in vivo in the rat.

To explore regional differences in triglyceride retention in white adipose tissues of growing male rats, the mass of adipocytes from epididymal, retroperitoneal, inguinal, and mesenteric tissues were followed with time. In order to attempt to explain regional differences, adipose tissue metabolism was studied in vivo and in vitro. (U-14C) oleic acid in sesame oil was given by gastric gavage to conscious male and female rats, and accumulation and half-life of radioactivity measured. Lipoprotein lipase activity and lipolysis were studied in vitro. Adipocyte triglyceride mass increased linearly in all the depots during 4 months of observation.The increase in mass was more pronounced in retroperitoneal (0.31 microg) and epididymal (0.30 microg) than in mesenteric (0.11 microg) or inguinal (0.05 microg) adipocytes. In the fed state label from (U-14C) oleic acid first increased with time in liver, muscle, and adipose tissues. In the liver radioactivity peaked at 4 hours, and was not measurable in either liver or muscle after a time point between 24 hours to 1 week. In contrast label continued to increase in adipose tissues up to about 16 hours to 24 hours, suggesting transfer of label by recirculation from liver and muscle to adipose tissues. Thereafter the radioactivity decreased. When expressed per adipocyte uptake of label was not significantly different between white adipose tissues. The rate of decrease between 7 days and 4 months was, however, more rapid in mesenteric and inguinal than, particularly, epididymal, and, probably, retroperitoneal adipocytes. These results were partly parallel to in vitro data on lipoprotein lipase activity, which was not different between depots, and the rate of lipolysis, which was higher in mesenteric than other adipocytes. These results suggest that differences in weight increase of adipose tissue regions are due mainly to differences in the rate of mobilization of adipocyte triglycerides. When expressed per gram triglyceride, uptake and mobilization of label were clearly more rapid in mesenteric than other white adipose tissues. This is probably explained by a combination of a higher adipocyte density plus the metabolic characteristics of adipocytes in this depot. Since mesenteric adipose tissue is smaller than the other depots studied, the absolute contribution of this tissue to the energy supply of the body is probably not different from that of other adipose tissues, however. A large uptake and short half life was observed in interscapular adipose tissue. This region contains brown adipocytes, and the results therefore suggest that lipid uptake for thermogenic purposes is of a considerable magnitude. It was concluded that among white adipose tissues, the mesenteric tissue has a rapid turnover of triglyceride. This is probably due to a combination of a high density and specific metabolic characteristics of these adipocytes. Factors in the microenvironment of adipocytes probably contribute to the high turnover either directly, or by modification of cellular characteristics.

Abdomen↗
PubMed1993

Crystal structure of TGF-beta 2 refined at 1.8 A resolution.

The crystal structure of TGF-beta 2 has been refined using data collected with synchrotron radiation (CHESS) to 1.8 A resolution with a residual R (= sigma magnitude of Fo-magnitude of Fc/sigma magnitude of Fo) factor of 17.3%. The model consists of 890 protein atoms from all 112 residues and 59 water molecules. The monomer of TGF-beta 2 assumes a rather extended conformation and lacks a well-defined hydrophobic core. Surface accessibility calculations show only 44% of the nonpolar surface is buried in the monomer. In contrast, 55.8% of the nonpolar surface area is buried when the two monomers form a dimer, a typical value for globular proteins. This includes a 1300 A2 buried interface area that is largely hydrophobic. Sequence comparisons using a profile derived from the refined TGF-beta 2 structure suggest that the cluster of four disulfides (three intramonomeric disulfide bonds 15-78, 44-109, 48-111 forming a disulfide knot, and one intermonomeric disulfide 77-77) together with the extended beta strand region constitutes the conserved structural motif for the TGF-beta superfamily. This structural motif, without the 77-77 disulfide bond, defines also the common fold for a general family of growth factors, including the nerve growth factor and platelet-derived growth factor families. The fold is conserved only at the monomer level, while the active forms are dimers, suggesting that dimerization plays an important role in regulating the binding of these cytokines to their receptors and in modulating the biological responses.

Crystallography, X-Ray↗
PubMed1993

Physical mapping of buzura suppressaria nuclear polyhedrosis virus genome.

A physical map of the genome of buzura suppressaria singly-enveloped nuclear polyhedrosis virus (BsSNPV) was determined using six restriction endonucleases (RE), singly or in pairs, and Southern hybridizations of cloned or gel-purified DNA fragments. The maps of the genomes of BsSNPV and autographa californica multiply-enveloped nuclear polyhedrosis virus (AcMNPV) were different.

Animals↗
PubMed1993

Effects of streptozotocin-induced diabetes mellitus and insulin treatment on neuropeptide Y mRNA in the rat hypothalamus.

Levels of neuropeptide Y and neuropeptide Y mRNA are increased in the arcuate nucleus of severely diabetic rats which may be the result of the associated marked hypoinsulinaemia. We hypothesised that if neuropeptide Y mRNA is regulated by physiological changes in circulating insulin, then the relatively minor changes in circulating insulin found in mild diabetes would also affect neuropeptide Y expression and its response to changing insulin levels should be rapid. Neuropeptide Y mRNA was quantified by in situ hybridisation through the rostral, mid and caudal levels of the arcuate nucleus of adult female rats. Neuropeptide Y mRNA was significantly increased at all three levels of the arcuate nucleus, 7 days after i.v. administration of 40 mg/kg streptozotocin. Neuropeptide Y mRNA was not further increased in the arcuate nucleus of animals given 50 mg/kg streptozotocin. In the former group, serum glucose was increased but insulin levels and body weights were the same as in control rats. In the 50 mg/kg streptozotocin group, serum glucose was further increased while serum insulin and body weight were reduced. In addition, neuropeptide Y mRNA was not altered in the hypothalamic dorsomedial nucleus or the thalamic reticular nucleus. When diabetic rats were treated for 20 h with s.c. insulin, there was decreased neuropeptide Y mRNA in the arcuate nucleus. We conclude that neuropeptide Y mRNA in the arcuate nucleus is responsive to small changes in circulating insulin levels and the response occurs within 20 h. These data support that circulating insulin may contribute to control of neuropeptide Y expression under physiological conditions.

Animals↗
PubMed1993

Application of computer-based histomorphometry to the quantitative analysis of methylprednisolone-treated adjuvant arthritis in rats.

Analyses of paw edema and histomorphometry were performed on tibio-talar joints to determine arthritic pathological responses in untreated 28-day adjuvant-induced polyarthritis (AIP) rats, and to determine the drug effect on inhibiting these responses in AIP rats treated with methylprednisolone. Histomorphometric measurements were performed on regions including articular joint space, synovial tissue, articular and epiphyseal cartilage, epiphyseal and metaphyseal bone marrow, and endosteal and periosteal cortical bone surfaces. Analysis of paw edema indicated that paw volume was significantly increased in untreated AIP rats. This increase in paw volume was partially prevented in AIP rats treated with 0.3 mg methylprednisolone/kg per day, and completely prevented in AIP rats treated with the two higher dose levels (1 and 3 mg/kg per day). Histomorphometric analysis of untreated AIP tibio-talar joints showed decreased articular joint space whereas synovial tissue area increased and a minor, but significant, articular cartilage erosion area occurred. Epiphyseal growth cartilage area was decreased. Trabecular bone area in distal tibial epiphyseal and metaphyseal regions was markedly decreased whereas bone marrow area increased involving a large number of macrophages and osteoclasts. Eroded endocortical bone area was increased while cortical bone area decreased. Marked osteophyte proliferation occurred on the periosteal surface. These arthritic pathological changes were inhibited by the treatment of methylprednisolone in a dose-dependent fashion. The animals treated with the highest dose of methylprednisolone complete prevented the development of the AIP-induced pathological changes. These data confirmed qualitative histological evaluation of arthritic changes but did not correlate with the anti-edema effects of methylprednisolone (100% inhibition at 1.0 and 3.0 mg/kg, p.o.). It is suggested that quantitative histomorphometry be used to determine more precisely the AIP rat model and the effects of drugs on different histopathological features in this experimental model of arthritis in preference to paw edema which gives a more limited picture of the arthritic response.

Analysis of Variance↗
PubMed1993

Prostaglandin E2 increased rat cortical bone mass when administered immediately following ovariectomy.

To investigate the effects of ovariectomy and the simultaneous administration of prostaglandin E2 (PGE2) on rat tibial shaft cortical bone histomorphometry, thirty-five 3-month-old female Sprague-Dawley rats were either ovariectomized (OVX), or sham ovariectomy (sham-OVX). The OVX rats were divided into three groups and treated with 0, 1 and 6 mg PGE2/kg/day for 90 days. The double fluorescent labeled undecalcified tibial shaft cross sections (proximal to the tibiofibular junction) of all the subjects were used for histomorphometry analysis. No differences in cross-sectional area and cortical bone area were found between sham-OVX and OVX controls, but OVX increased marrow area, intracortical porosity area and endocortical eroded perimeter. Periosteal and endocortical bone formation rates decreased with aging yet OVX prevented these changes. These OVX-induced increases in marrow area and endocortical eroded perimeter were prevented by 1 mg PGE2/kg/day treatment and added bone to periosteal and endocortical surfaces and to the marrow cavity. At the 6 mg/kg/day dose level, PGE2-treated OVX rats increased total tissue area, cortical bone area, marrow trabecular bone area, minimal cortical width and intracortical porosity area, and decreased marrow area compared to basal, sham-OVX and OVX controls. In addition, periosteal bone formation was elevated in the 6 mg PGE2/kg/day-treated OVX rats compared to OVX controls. Endocortical eroded perimeter increased from basal and sham-OVX control levels, but decreased from OVX control levels in the 6 mg PGE2/kg/day-treated OVX rats. Our study confirmed that ovariectomy does not cause osteopenia in tibial shaft cortical bone in rats, but it does stimulate endocortical bone resorption and enlarges marrow area. The new findings from the present study demonstrate that PGE2 prevents the OVX-induced increases in endocortical bone resorption and marrow area and adds additional bone to periosteal and endocortical surfaces and to marrow cavity to increase total bone mass in the tibial shaft of OVX rats when given immediately following ovariectomy.

Animals↗
PubMed1993

Influence of somatostatin analogue (SMS 201-995, octreotide) on blood pressure in adrenocorticotrophin (ACTH) treated rats: role of hyperinsulinaemia in ACTH hypertension.

1. The hypothesis that adrenocorticotrophin (ACTH)-induced hypertension is a consequence of steroid-induced hyperinsulinaemia was tested using the somatostatin analogue (sandostatin, octreotide) to inhibit insulin release in Sprague-Dawley (SD) rats (n = 41). 2. Octreotide (20 micrograms, twice daily) did not modify blood pressure, plasma glucose, bodyweight, water and electrolyte balance, or organ weights but inhibited insulin secretion in the SD rat. 3. Compared with sham injection, ACTH-treated (0.5 mg/kg per day) SD rats showed an increase in blood pressure (sham 111 +/- 4 mmHg; ACTH 140 +/- 5 mmHg on treatment day 10 (P < 0.01), organ weights, water intake, urine volume, plasma glucose, insulin and sodium concentrations, and decrease of bodyweight and plasma potassium concentration. 4. Systolic blood pressure in rats treated with combined octreotide and ACTH was similar to that in rats on ACTH alone. Plasma insulin concentration was lower in octreotide + ACTH treated rats than with ACTH treatment alone. There were no differences in body or organ weights, plasma glucose, water or electrolyte balance. 5. Octreotide lowered plasma insulin concentration to the normal range but did not modify ACTH-induced hypertension in SD rats. These data do not support the notion that insulin-mediated alterations in blood pressure are a major mechanism for ACTH-induced hypertension in the rat.

Adrenocorticotropic Hormone↗
PubMed1993

A cis element required for induction of the interleukin 2 enhancer by human T-cell leukemia virus type I binds a novel Tax-inducible nuclear protein.

The 40-kDa nuclear protein Tax encoded by human T-cell leukemia virus type I (HTLV-I) can transcriptionally activate the interleukin 2 (IL-2) enhancer even in the presence of the immunosuppressant cyclosporin A, which inhibits the activation of the IL-2 enhancer by T-cell mitogens. We have identified a Tax-responsive element (TxRE) from -164 to -145 bp in the IL-2 enhancer which is sufficient to confer Tax responsiveness. A 45-kDa nuclear protein (TxRE-binding factor [TxREF]), present in Tax-expressing Jurkat cell lines but not in Jurkat cells without Tax, specifically interacts with the 5' TxRE sequence from -164 to -154. Deletion or mutation of this 5' TxRE sequence removes the binding of TxREF in vitro and dramatically reduces Tax activity in vivo. In addition, this site is responsible for the cyclosporin A-resistant expression of the IL-2 enhancer in the presence of Tax. Although the TxREF binding site contains an NF-kappa B like motif, UV cross-linking studies as well as gel retardation analysis reveal that TxREF is distinct from NF-kappa B. These results demonstrate that TxREF is a novel Tax-inducible DNA-binding protein and that TxRE plays a crucial role in mediating Tax-induced IL-2 gene expression.

Base Sequence↗
PubMed1993

Iodine induced lymphocytic thyroiditis in the BB/W rat: early and late immune phenomena.

The effect of iodine excess on thyroid function and on the immunological sequence of events leading to lymphocytic thyroiditis (LT) was studied in the NB subline of BB/W rats to determine the mechanisms by which the level of iodine intake influences the development of LT in this animal model. Iodine supplemented water (500 micrograms/l, Group 1 or 500 mg/l, Group 2) or non-iodine supplemented tap water (Group 3) was given to breeding pairs and their offspring ad libitum. A Wistar rat group, also given tap water (Group 4) served as controls. To determine the immunological sequence of events, the phenotypic nature of the infiltrating thyroid lymphocytes was examined by specific immunoperoxidase staining in BB/W and Wistar rats at 6, 9, 12, and 15 weeks. Antigen-presenting cells and class II (Ia) antigen expression on thyrocytes were also examined. The first immunological event apparent in the iodine-treated BB/W rats was a sharp increase in the number of Ia positive dendritic cells at 9 weeks compared with control BB/W and Wistar rats. In the iodine excess groups dendritic cells were associated with scattered areas of lymphocytic infiltration, comprising predominantly T helper cells (W3/25). T suppressor cells (OX 8) and IL-2 receptor positive activated T-cells (OX 39) were both present in small numbers. B-cells (OX 12) were absent. In addition, thyrocytes did not exhibit Ia antigen expression. By contrast, lymphocytic infiltration was not found at 9 weeks in control BB/W rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Studies on immobilization of aminoacylase on the functionalized polymethyl acrylate.

Functionalized polymethyl acrylate was used for the immobilization of aminoacylase of Aspergillus oryzae. The effects of the degree of cross-linking, the amount of pore-forming agent and their mixing rates on the activity of immobilized aminoacylase were investigated. The results showed that the activity of the immobilized aminoacylase was the highest when the carrier was a combination of 20% cross-linking and 100% pore-forming agent. The effects of substrate concentration, ionic concentration, temperature and pH on the immobilized aminoacylase were compared with those on soluble aminoacylase, on the other hand, the effects of some organic solvents and protein denaturants on immobilized aminoacylase were also investigated. A column reactor packed with immobilized aminoacylase was used to resolve continuously N-acyl-DL-phenylalanine for a month, and 90% activity of immobilized aminoacylase was retained.

Amidohydrolases↗
PubMed1993

Glomerulonephritis induced by human IgMK-IgG cryoglobulins in mice.

BACKGROUND: Human cryoglobulinemia is sometimes associated with glomerulonephritis (GN) due to deposition of cryoglobulins (cryos). To see whether human cryos can induce GN in mice and to study time-related changes of glomerular lesions and possible factors of cryos' nephritogenicity, we developed an experimental passive model of cryoglobulinemic GN. EXPERIMENTAL DESIGN: Two cryos IgMk-IgG from 2 patients with active GN (OLD and SOR), 2 cryos IgMk-IgG (TAC and GRO) and 1 IgM lambda (CHI) from 3 patients without GN were purified, solubilized at 37 degrees C and injected intravenously into BALB/c mice, 4 mg, twice a day. To study the possible factors of cryo nephritogenicity, we analyzed: (a) the presence, amount, and size of complexed IgMk-IgG at 37 degrees C by fast flow liquid chromatography; (b) the Cc1 or Lc1 subclass of rheumatoid factors; (c) the isoelectric points of the IgMks; (d) The proportion of IgG subclasses in cryos. RESULTS: On day 1 from the beginning of intravenous injections, cryos OLD had induced mesangial deposits of human IgM, human IgG, mouse C3 and mesangial hypercellularity. On day 2, phagocytizing cells were found along with massive endoluminal and subendothelial deposits of IgM, IgG, and C3. On day 6, perivascular infiltrates of mononuclear cells were also seen. Cryos SOR induced a similar but milder form of GN. After administration of purified OLD IgMk, OLD IgG, GRO IgMk or GRO IgG, only OLD IgMk was deposited in the mesangium. Analysis of all the cryos revealed that: the amount of complexed IgMk-IgG at 37 degrees C was always less than 1% of cryos; Cc1 and Lc1 idiotypes were not related to the nephritogenicity of cryos, the isoelectric points of IgMks were 4.5 to 5.5 and IgG1 was the prevalent subclass. CONCLUSIONS: Data demonstrate that human cryos from patients with GN can induce GN in mice that resembles the corresponding human pathology. The affinity of IgMk for glomeruli and the unexpectedly small amounts of IgMk-IgG complexes at 37 degrees C suggest that there is a role of in situ binding in nephritogenicity which is independent of the isoelectric point, rheumatoid factor idiotype, or IgG subclass.

Aged↗
PubMed1993

[Development of hybridomas secreting monoclonal anti-idiotypic antibodies that bear the internal image of the terminal trisaccharide of PGL-I].

Two hybridomas designated as F7B7 and F7B9 secreting monoclonal anti-idiotypic antibodies against terminal trisaccharide of PGL-I were developed by fusion of SP2/0 cells and spleen cells of BALB/c mouse immunized with mouse monoclonal anti-trisaccharide of PGL-I (MAb1-E10F1). To characterize the F7B7, the following results were obtained. First, F7B7 reacted with MAb1-E10F1 specifically. Secondly, the cross ELISA neutralizing tests gave positive results. The binding of anti-trisaccharide positive serum with trisaccharide (contained in semi-synthetic antigen, NT-O-BSA) was inhibited F7B7 and the degree of inhibition showed dose-dependent manner. The binding of anti-trisaccharide positive serum with F7B7 was inhibited by NT-O-BSA and the degree of inhibition also showed dose-dependent manner. It was concluded that the hybridoma F7B7 is able to secrete monoclonal anti-idiotypic antibodies that bear the internal image of trisaccharide of PGL-I. The potentials and advantages of monoclonal anti-idiotypic antibody F7B7 as surrogate antigen in the serodiagnosis of leprosy have been discussed.

Animals↗
PubMed1993

Assay of inert gas contamination in studies of hydrostatic pressure effects.

In hyperbaric tissue studies it is common to use gas pressure as a means for increasing the hydrostatic pressure of the preparation. When this is done, one must take the necessary precautions to avoid gas contamination of the tissue. In the present study, we demonstrate a) methods for calculating the gas contamination using particular materials in the perfusion system, and b) a technique for isolating the fluid environment from contamination by the compressing gas in a flow-through tissue chamber. The present work is exemplified with a specific apparatus, but the general principle is applicable to other studies.

Atmosphere Exposure Chambers↗
PubMed1993

Development of antisera selective for m4 and m5 muscarinic cholinergic receptors: distribution of m4 and m5 receptors in rat brain.

A portion of the cDNA sequence corresponding to the third intracellular loop of either the m4 or m5 muscarinic cholinergic receptor was ligated into the pRIT23 or pET-3a expression vector, respectively. The expressed fusion proteins were purified and used to develop selective polyclonal antisera to the m4 and m5 muscarinic receptors. These antisera were used in an immunoprecipitation protocol to examine quantitatively the distribution of receptor subtypes in regions of rat brain. The density of m4 receptors in rat brain increased in the caudal to rostral direction. The highest levels of m4 receptors were detected in the striatum (1280 fmol/mg) and olfactory tubercle (750 fmol/mg). Low levels of m5 receptors were detected in several brain regions (< 25 fmol/mg). By combining the previously determined receptor densities for the m1, m2, and m3 receptors and results obtained with the newly developed antisera to m4 and m5 receptors, it was determined that 86-99% of the [3H]quinuclidinyl benzilate binding sites in several brain regions were immunoprecipitated. In addition to measuring receptor densities in rat brain, the immunoprecipitation protocol was used to quantify muscarinic receptor levels in tissues reported to express mRNA encoding the m4 receptor. Thus, although only m4 mRNA has been detected in rabbit lung, NG108-15 cells, and N1E-115 cells, both rabbit lung and NG108-15 cells possess both m2 (rabbit lung, 27%; NG108-15 cells, 31%) and m4 (rabbit lung, 55%; NG108-15, 42%) receptors, whereas N1E-115 cells were found to have both m1 (15%) and m4 (65%) receptors. These antisera will be useful in studies of receptor regulation and in determining alterations in density that may occur after pharmacological or physiological manipulations and in various disease states.

Animals↗