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Biomedical subjects

H L Li

Publications and source records attributed to H L Li.

At least 73 records · Page 4Linked to original sources
PubMed1997

Nasal administration of myelin basic protein prevents relapsing experimental autoimmune encephalomyelitis in DA rats by activating regulatory cells expressing IL-4 and TGF-beta mRNA.

This study explores nasal administration of myelin basic protein (MBP) as a potential means of inducing tolerance to relapsing experimental autoimmune encephalomyelitis (PR-EAE), an experimental multiple sclerosis (MS) model that was induced in DA rats by immunization with rat spinal cord homogenate and incomplete Freund's adjuvant. DA rats received a total dosage of 0, 6, 60, 600 micrograms/rat of bovine MBP on ten consecutive days prior to immunization. EAE with typical course was observed in control rats receiving only PBS nasally, and in rats receiving 6 micrograms/rat of MBP. Rats receiving 60 micrograms/rat of MBP developed acute EAE but no relapse during 60 days of observation post immunization (p.i.). Only one of eight rats receiving 600 micrograms/rat of MBP developed slight, transient EAE. This protection was confirmed at the histology level and was associated with decreased levels of MBP-reactive IFN-gamma secreting Th1-like spleen cells on day 13 and 60 p.i. Rats receiving 60 and 600 micrograms/rat of MBP showed decreased serum anti-MBP IgG2b antibody levels on day 60 p.i., and rats receiving 600 micrograms/rat of MBP had marginally increased anti-MBP IgG1 antibody levels in serum compared to control EAE rats. Cytokine mRNA profiles in central nervous system (CNS) and spleen mononuclear cells were evaluated. Dose-dependent reduction of TNF-alpha mRNA expression were observed both in CNS and in splenocytes. Increased IL-4 and TGF-beta mRNA expression were observed in CNS of low (6 micrograms/rat) and median (60 micrograms/rat) dose of MBP tolerized rats and in splenocytes of rats tolerized with 600 micrograms/rat of MBP. We conclude that nasal administration of MBP in DA rat prevents EAE induced by immunization with whole rat spinal cord homogenate that, besides MBP, contains multiple antigenic myelin proteins. A mechanism involving MBP-reactive regulatory cells expressing IL-4 and TGF-beta mRNA acts as part in the induction of this tolerance.

Administration, Intranasal↗
PubMed1997

Ultraviolet A irradiation upregulates type VII collagen expression in human dermal fibroblasts.

Type VII collagen, a major component of skin-anchoring fibrils, is synthesized by both fibroblasts and keratinocytes, the two principal cell types in the skin. In this study, we examined the effects of ultraviolet A (UVA) irradiation on the expression of type VII collagen in human fibroblasts. UVA irradiation (0-15 J/cm2) caused a dose-dependent increase (5- to 10-fold) in type VII collagen mRNA levels as detected by northern blot analysis. The UVA-induced enhancement of type VII collagen gene expression correlated with an increase in its protein level by immunoblot analysis of proteins secreted into the conditioned medium. The effect of UVA was observed at 12 h and reached its maximum by 18 h. Under these conditions, however, the expression of fibronectin, a major dermal matrix protein, remained unchanged, suggesting that the induction of type VII collagen expression was selective. Actinomycin D, a transcription inhibitor, blocked the UVA-mediated induction of type VII collagen gene expression, whereas cycloheximide, a protein synthesis inhibitor, superinduced the expression of type VII collagen, suggesting that de novo protein synthesis was not required for the action of UVA. Interestingly, in contrast to the increased type VII collagen expression in fibroblasts in response to UVA, a slight decrease in type VII collagen mRNA level was observed in the UVA-irradiated keratinocytes, suggesting that the effect of UVA on the type VII collagen expression is cell type specific.

Adult↗
PubMed1997

Defective neurite extension is caused by a mutation in amyloid beta/A4 (A beta) protein precursor found in familial Alzheimer's disease.

Clonal central nervous system neuronal cells, B103, do not synthesize detectable endogenous APP or APLP. B103 cells transfected with both wild-type (B103/APP) and mutant APP construct (B103/APP delta NL) secreted comparable amounts of soluble forms of APP (sAPP). B103/APP cells produced sAPP and cleaved at amyloid beta/A4 (A beta) 16, the alpha-secretase site, and B103/APP delta NL cells produced sAPP beta cleaved at A beta 1, the beta-secretase site. B103/APP delta NL cells developed fewer neurites than B103/APP cells in a serum-free defined medium. Neurite numbers of parent B103 cells were increased by the 50% conditioned medium (CM) from B103/APP cells but reduced by the CM from B103/APP delta NL cells. Chemically synthesized A beta at concentration levels higher than 1 nM reduced numbers of neurites from B103 or B103/APP delta NL cells. However, A beta at 1-100 nM could not reduce the neurite number of B103/APP cells. The protective activity against A beta's deleterious effect to reduce neurite numbers was attributed to sAPP alpha in the CM. Although sAPP alpha could block the effect of A beta, sAPP beta could not do so under the identical condition, suggesting the importance of the C-terminal 15-amino acid sequence in sAPP alpha. Nevertheless, sAPP alpha's protective activity required the N-terminal sequence around RERMS, previously identified to be the active domain of sAPP beta. The overall effect of APP mutation which overproduced A beta and sAPP beta and underproduced sAPP alpha was a marked decline in the neurotrophic effect of APP. We suggest that the disruption of balance between the detrimental effect of A beta and the trophic effect of sAPP may be important in the pathogenesis of AD caused by this pathogenic APP mutation.

Alzheimer Disease↗
PubMed1996

Alcohol inhibits the depolarization-induced stimulation of oxidative phosphorylation in synaptosomes.

The effects of alcohol and Ca2+ transport inhibitors on depolarization-induced stimulation of oxidative phosphorylation and free-Ca2+ concentrations in rat synaptosomes were investigated. Glucose oxidation was stimulated by depolarization with K+ or veratridine and by the Ca2+ ionophore ionomycin. The stimulation by K+, veratridine, and ionomycin was correlated with elevation of synaptosomal free Ca2+. Depolarization-stimulated respiration was inhibited by verapamil, Cd2+, and ruthenium red but not by diltiazem. Synaptosomal Ca2+ elevation was inhibited by verapamil but not by ruthenium red. These results indicate that the stimulation depends on elevation of mitochondrial free Ca2+. Ethanol, at pharmacological concentrations (50-200 mM), inhibited the Ca2+-dependent stimulation of oxidative phosphorylation. This inhibition resulted, in part, from the inhibition of voltage-gated Ca2+ channels, which inhibited the elevation of synaptosomal free Ca2+, and, in part, from the stimulation of the mitochondrial Ca2+/Na+ antiporter, which inhibited the elevation of the mitochondrial matrix free Ca2+. The inhibition by ethanol of the excitation-induced stimulation of oxidative phosphorylation in the synapse may contribute to the depressant and narcotic effects of alcohol and enhance excitotoxicity.

Adenosine Triphosphate↗
PubMed1996

[Effect of integrated Chinese medicine on early stage of acute cerebral hemorrhage].

The effect of integrated Chinese medicine (ICM) on the convalescent of acute cerebral hemorrhage patients were observed. The results showd that the effect of patients treated with ICM was better than that treated with Western medicine alone on the aspects of absorption of brain hemetoma, elimination of encephaledema and recovery of neural function (P < 0.05, 0.01). It suggested that early application of integrated Chinese medicine is very helpful in rehabilitation of cerebral hemorrhage patients.

Acute Disease↗
PubMed1995

Alcohol inhibits the activation of NAD-linked dehydrogenases by calcium in brain and heart mitochondria.

The effect of ethanol on the Ca(2+)-dependent activation of mitochondrial dehydrogenases in rat brain and heart mitochondria was investigated. ADP-stimulated respiration of isolated brain and heart mitochondria (state 3) was stimulated further by submicromolar concentrations of free calcium when respiring on non-saturating concentrations of NAD-linked substrates. The stimulation of oxidative phosphorylation by Ca2+ was correlated with an increase of the mitochondrial matrix free calcium concentration ([Ca2+]m), as measured by fura-2, and with an increased reduction of the mitochondrial NAD(P) pool, indicating an activation of Ca(2+)-dependent dehydrogenases. Sodium inhibited Ca(2+)-dependent stimulation of state 3 respiration and NAD(P) reduction as a result of stimulation of Ca2+ efflux through the Na+/Ca2+ antiporter which reduced the steady-state value of [Ca2+]m. Ethanol stimulated the Na+/Ca2+ antiporter both in brain and heart mitochondria. As a result of this stimulation, ethanol, at pharmacological concentrations (50-300 mM), enhanced the sodium-dependent reduction of [Ca2+]m, and thus attenuated the activation of NAD-linked dehydrogenases and the stimulation of oxidative phosphorylation, by submicromolar concentrations of Ca2+, both in brain and heart mitochondria. This pharmacological effect of ethanol, on brain and heart mitochondria, may be responsible, in part, for the acute and chronic effects of ethanol on brain and heart function and metabolism.

Alcohol Oxidoreductases↗
PubMed1995

Regulation and inhibition of collagenase expression by long-wavelength ultraviolet radiation in cultured human skin fibroblasts.

The cellular mechanisms responsible for the connective tissue changes produced by chronic exposure to UV light are poorly understood. Collagenase, a metalloproteinase, initiates degradation of types I and III collagen and thus plays a key role in the remodeling of dermal collagen. Collagenase synthesis by fibroblasts and keratinocytes involves the protein kinase C (PKC) second messenger system, and corticosteroids have been shown to suppress its synthesis at the level of gene transcription. Long-wavelength UV light (UVA, 320-400 nm) stimulates the synthesis of interstitial collagenase, as well as increasing PKC activity, in human skin fibroblasts in vitro. This study explores the regulation of collagenase expression by UVA in cultured human skin fibroblasts. Specifically, the time course, the effect of actinomycin D, an inhibitor of RNA synthesis, as well as the effect of PKC inhibitors and dexamethasone on expression of collagenase following UVA irradiation were examined. After UVA irradiation, collagenase mRNA rose rapidly between 4 and 12 h postirradiation, peaking 18 h post-UVA. Actinomycin D completely suppressed the UVA-induced increase in collagenase mRNA. Thus, new RNA synthesis is required for the UVA-induced increase in collagenase mRNA. The PKC inhibitor, H-7, blocked the increase in collagenase mRNA in response to UVA in a dose-dependent manner. Similarly, dexamethasone also inhibited collagenase gene expression induced by UVA in a dose-dependent fashion; the majority of the inhibitory effect was seen within the first 4 h after irradiation. These studies demonstrate that the effect of UVA on collagenase gene expression is regulated at the pretranscriptional level and may involve the PKC pathway.

Cells, Cultured↗
PubMed1994

Human insulin-like growth factor I receptor internalization. Role of the juxtamembrane domain.

Cytoplasmic submembrane domains of the insulin-like growth factor I (IGF-1) receptor ranging from glycine 940 to proline 959 were investigated for their role in endocytosis of the IGF-1 ligand in rat pituitary GC cells stably expressing mutant human IGF-1 receptors. Replacement of each of three tyrosine residues within the juxtamembrane domain reduced the internalization rate (Ke) by 33% (943Y-->A), 47% (950Y-->A), and 41% (957Y-->A), respectively. Other substitutions within the submembrane region variably retarded receptor-mediated IGF-1 ligand endocytosis. Thus, each amino acid appears to independently contribute to the overall ligand-stimulated IGF-1 receptor internalization rate. The effect of receptor occupancy on IGF-1 receptor endocytosis was also tested. The rate of 125I-labeled IGF-1 internalization by transfectants overexpressing the wild type IGF-1 receptor was rapid but decreased markedly in the presence of increasing unlabeled IGF-1 (ED50 = 44,000 receptors/cell). Substitution by alanine for any of the three submembrane tyrosines increased the ED50 to > 56,000 receptors/cell, decreased the slope (Kic), and had a variable effect on Vmax in the presence of increasing unlabeled IGF-1. In contrast, 125I-labeled IGF-1 endocytosis by the mutant kinase-deficient 952STOP cells was slow and not further retarded by unlabeled IGF-1. These results suggest that ligand-mediated internalization of the human IGF-I is consistent with saturable interactions between the IGF-I receptor juxtamembrane region (glycine 940-tyrosine 957) and components of the endocytic apparatus.

Amino Acid Sequence↗
PubMed1994

Dominant negative inhibition of tumorigenesis in vivo by human insulin-like growth factor I receptor mutant.

Although insulin-like growth factor I (IGF-I) is a mitogenic growth factor, its role in tumorigenesis is unclear. We therefore transfected wild-type and truncated beta-subunit mutant (952STOP) human IGF-I receptor cDNAs into Rat-1 fibroblasts. Rat-1 transfectants expressed 2.5- to 7-fold increased IGF-I receptor mass, while the Kd for IGF-I binding was unchanged. The Rat-1 cells transfected with wild-type receptor cDNA responded to in vitro IGF-I treatment by increased proliferation and DNA synthesis. Cells overexpressing wild-type receptors were also transformed as evidenced by ligand-dependent colony proliferation in soft agar. After injection into athymic nude mice, all wild-type transfectants formed solid sarcomas within 3 weeks, and ex vivo tumor cell assays confirmed continued overexpression of human IGF-I receptors. In contrast, both DNA synthesis and proliferation of 952STOP-transfected cells were attenuated below that of untransfected cells. 952STOP cells were nonresponsive to IGF-I in vitro and were unable to sustain anchorage-independent growth. No tumors were induced for up to 8 weeks after injection of 952STOP transfectants into athymic mice, despite the presence of demonstrable endogenous IGF-I receptors on the 952STOP-transfected cells. Therefore, 952STOP behaves as a dominant negative inhibitor of endogenous IGF-I receptor function, probably by assembling nonfunctional hybrid rat/mutant human receptor tetramers.

Animals↗
PubMed1994

Genetically modified skin to treat disease: potential and limitations.

Molecular definition of disease at the level of the gene and advances in recombinant DNA technology suggest that many diseases are amenable to correction by genes not bearing the defective elements that result in disease. Many questions must be answered before this therapy can be used to correct chronic diseases. These questions fall into safety and efficacy categories. Experience with transplanting cellular elements of skin or skin substitutes (defined as skin that possess the cell types and a dermal structure to develop into a functioning skin) to athymic rodents is considerable and is seen as a system where these questions can be answered. This paper reviews these questions and presents our early analysis of genetically modified cells in skin substitutes in vivo and in vitro. Experimental data demonstrate that both a matrix of woven nylon, housing a fibroblast generated collage, and dead dermis can be utilized to shuttle genetically modified human fibroblasts from the laboratory to an in vivo setting. Genetically modified fibroblasts do not migrate from the shuttle to the surrounding tissue. The survival of significant numbers, approximately 70%, of genetically modified fibroblasts for at least 6 weeks in these shuttles, supports this general approach as having clinical utility. It is also concluded that skin substitute systems can be used to generate a genetically modified skin in vitro that has the capacity to develop into functional skin in vivo. Further, as genetically modified keratinocytes differentiate there is increased production by the transgene, supporting the concept that keratinocytes have true potential as shuttles for therapeutic genes. This work demonstrates that transplantation of systems containing genetically modified cells of the skin can be used to experimentally define many aspects of gene therapy using skin before this technology is taken to the clinic. Examples include determining the effect of gene transduction and expression on structure and function of the genetically modified skin as well as on distant skin and an assessment of the translational capacity of the transgene as function of time and cell number.

3T3 Cells↗
PubMed1994

Human papillomavirus in condyloma acuminata and other benign lesions of the female genital tract.

PCR was used to detect (HPV) in condyloma acuminata (CA), pseudocondyloma whose cause is unclear, and the other benign lesions in female genital tract. The results showed that HPV prevalence rate in CA was 98.2%, type 6 was in 11 was 85.7%, and that in pseudocondyloma, cervical polyp, cervical erosion and chronic vaginitis was 40.4%, 76.2%, 77.3% and 16.0%, respectively. Even in normal vaginal tissue, there existed HPV subclinical infection. HPV prevalence rate in swabs from patient's underwears and normal vaginal tissues was 73.6% and 54.0% respectively. The investigation of estrogen receptor (ER) in CA tissue carried out by immunohistochemical method found that positive ER was achieved in most of CA, and few of normal vulvar tissues was found. This result indicated that the occurrence of CA is probably related to estrogen.

Condylomata Acuminata↗
PubMed1994

[Whole embryo culture for detecting teratogen].

Whole embryo culture technique was used to study direct effects of Penicillin G, Thiadiazole, Actinomycin D and glucose solution of high concentration on the development and growth of rat embryos, without maternal and placental influence. Nine-and-a-half-day rat embryos were transplanted to culture flasks from the animal's wombs for in vitro culture, and the four chemicals were added to culture medium, respectively. Results showed all those chemicals could cause death and malformation of the embryos and retardation in embryonic development and growth cultured in vitro, with an apparent dose-effect relationship. The embryonic malformations caused by the chemicals were the same both in vitro culture and in vivo. Possible teratogenesis of the chemicals and survival of the malformed embryos were speculated based on the above dose-effect relationship.

Animals↗
PubMed1993

Ribonuclease III cleavage of a bacteriophage T7 processing signal. Divalent cation specificity, and specific anion effects.

Escherichia coli ribonuclease III, purified to homogeneity from an overexpressing bacterial strain, exhibits a high catalytic efficiency and thermostable processing activity in vitro. The RNase III-catalyzed cleavage of a 47 nucleotide substrate (R1.1 RNA), based on the bacteriophage T7 R1.1 processing signal, follows substrate saturation kinetics, with a Km of 0.26 microM, and kcat of 7.7 min.-1 (37 degrees C, in buffer containing 250 mM potassium glutamate and 10 mM MgCl2). Mn2+ and Co2+ can support the enzymatic cleavage of the R1.1 RNA canonical site, and both metal ions exhibit concentration dependences similar to that of Mg2+. Mn2+ and Co2+ in addition promote enzymatic cleavage of a secondary site in R1.1 RNA, which is proposed to result from the altered hydrolytic activity of the metalloenzyme (RNase III 'star' activity), exhibiting a broadened cleavage specificity. Neither Ca2+ nor Zn2+ support RNase III processing, and Zn2+ moreover inhibits the Mg(2+)-dependent enzymatic reaction without blocking substrate binding. RNase III does not require monovalent salt for processing activity; however, the in vitro reactivity pattern is influenced by the monovalent salt concentration, as well as type of anion. First, R1.1 RNA secondary site cleavage increases as the salt concentration is lowered, perhaps reflecting enhanced enzyme binding to substrate. Second, the substitution of glutamate anion for chloride anion extends the salt concentration range within which efficient processing occurs. Third, fluoride anion inhibits RNase III-catalyzed cleavage, by a mechanism which does not involve inhibition of substrate binding.

Anions↗
PubMed1993

[Establishment of two cell lines secreting monoclonal antibodies against pathogenic free-living amoeba in Shanghai].

Taking Naegleria australiensis, a species of pathogenic free-living amoeba (isolated in Shanghai in 1986), as antigen, two cell lines which provided potentially permanent source of monoclonal antibodies were established by lymphocytic hybridoma technique. The results of identification showed that: (1) the two cell lines could secret two different kinds of McAbs; (2) both of the McAbs were IgG (by gel diffusion); (3) McAbs produced in BALB/c mice were at high concentrations. One of them had a titer of > or = 1:8,192 and the other > or = 1:1,024 (by enzyme linked immunosorbent assay). A decline of the titers after purification by salting-out method was shown. One of the purified McAbs had a titer of > or = 1:2,024 and the other > or = 1:128. We have adopted two ways of recovering cryopreserved cells: ordinary recovering and "direct" recovering. The latter way was more practical because it could reduce the cycle of antibody production, and avoid contamination and chromosome variation. Experiments with different doses of cells revealed that, if the latter way was used, the optimal dose was 3 to 5 x 10(6) cells per mouse.

Animals↗
PubMed1992

Antiplatelet actions of some coumarin compounds isolated from plant sources.

Xanthyletin, xanthoxyletin, suberosin (all from Citrus grandis), aurapten (from Severinia huxifolia) and poncitrin (from Poncirus trifoliata) were isolated and their chemical structures were characterized to be coumarin compounds. All these coumarin compounds except xanthyletin inhibited the aggregation and ATP release of rabbit platelets induced by arachidonic acid, collagen, ADP, platelet-activating factor (PAF) or U46619 (a thromboxane A2 analog). Thrombin-induced ATP release, but not the aggregation, was also inhibited by these compounds. Xanthyletin inhibited only platelet aggregation induced by arachidonic acid and collagen, while poncitrin inhibited that caused by PAF more markedly than other coumarin compounds. The thromboxane B2 formation in washed platelets caused by arachidonic acid and collagen was suppressed by these coumarin compounds. The phosphoinositide breakdown caused by collagen and PAF was also inhibited by these compounds. They did not affect fibrinogen-induced aggregation of elastase-treated platelets. These antiplatelet actions were immediate, reversible by washout and independent on the incubation time (except suberosin). Antiaggregating effect was also studied by an electrical impedance method and the inhibitory effect of coumarin compounds on the whole blood and platelet-rich plasma was much less than that of platelet suspension in the aggregation induced by collagen, PAF and ADP. It is concluded that the antiplatelet actions of these coumarin compounds are due to the inhibition on thromboxane A2 formation and phosphoinositides breakdown.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1992

Resistance to ethanol disordering of membranes from ethanol-fed rats is conferred by all phospholipid classes.

Phospholipids extracted from liver microsomes and mitochondria of ethanol-fed rats retained the resistance to membrane disordered by ethanol which is observed in the intact isolated membranes. The lipid extracts were separated into the major phospholipid classes (phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol from microsomes and phosphatidylcholine, phosphatidylethanolamine and cardiolipin from mitochondria) by preparative TLC. The extent of membrane disordering by ethanol of phospholipid vesicles composed of a mixture of phospholipids from ethanol-fed rats and controls was determined from the reduction of the order parameter of the spin-probe 12-doxyl-stearate. In contrast to previous reports, we found that all phospholipid classes from ethanol-fed rats confer resistance to disordering by ethanol. To a first approximation the extent of resistance was proportional to the fraction of lipids from ethanol-fed rats, regardless of the phospholipid head-group. Subtle differences between phospholipid classes may exist but were too small to measure accurately. Except for phosphatidylethanol, incorporation of anionic phospholipids did not have a significant effect on the sensitivity of phospholipid vesicles to the disordering effect of ethanol. Vesicles prepared from mixtures of various dioleoyl phospholipids and natural phospholipids did not indicate a clear effect of fatty acid saturation on the sensitivity to disordering by ethanol. Although the precise molecular changes that occur in phospholipids from ethanol-fed rats have not been fully characterized it appears that subtle changes in all phospholipid classes contribute to the resistance to ethanol disordering of these membranes.

Administration, Oral↗