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Biomedical subjects

L Lin

Publications and source records attributed to L Lin.

At least 289 records · Page 16Linked to original sources
PubMed1994

Nephrotoxicity of low doses of tobramycin in rats: effect of the time of administration.

The circadian and the circannual variations of the nephrotoxicity of tobramycin were studied in female Sprague-Dawley rats. Animals were maintained on a light-dark period of 14/10 hrs (light on: 06h00 to 20h00). They were injected once daily for 4 and 10 days with saline or tobramycin at a dose of 40 mg/kg/day i.p. at either 08h00, 14h00, 20h00 and 02h00, in April 1991, July 91, October 91, January 92. In April 91, tobramycin injected at 14h00 during 10 days induced a significant increase of [3H]-thymidine incorporation into DNA of renal cortex as compared to other groups (p < 0.01): toxicity was highest at 14h00 and lowest at 02h00. No temporal change was observed in the renal cortical accumulation of tobramycin, and in serum creatinine after the 4 or 10 days of treatment. In experiments done in April, July and October 1991 and in January 1992, no circannual variation was found in tobramycin cortical levels but peaks of toxicity were observed at 02h00 in April and October 1991 and at 14h00 in July 1991 and January 1992. There was no linear correlation between the toxicity and the tobramycin accumulation in the renal cortex (r = 0.21). The data suggest that the circadian changes in tobramycin toxicity are due to temporal changes in the susceptibility of renal cells to tobramycin.

Animals↗
PubMed1994

Structural requirements for the biological activity of enterostatin.

A series of enterostatin analogues were tested to investigate the minimal structure required for activity to suppress the intake of high-fat (HF) diets. The dose-response curve to intracerebroventricular (ICV) enterostatin was U-shaped (maximal inhibition at 1 nmol). Removal or modification of the N-terminal valine from enterostatin (Val-Pro-Asp-Pro-Arg) abolished activity, as did C-terminal amidation. The tripeptide (Pro-Asp-Pro) and the cyclo-diketopiperazine cyclo-Asp-Pro retained activity whereas the linear Asp-Pro dipeptide was inactive. In rats adapted to a three-choice macronutrient diet, cyclo-Asp-Pro specifically inhibited fat intake and had near maximal inhibition (50%) at the 0.03 nmol dose. The enterostatin inhibitory effect on fat intake may reside in the cyclo-diketopiperazine molecule, cyclo-Asp-Pro.

Amino Acid Sequence↗
PubMed1994

Ganglioside GM1 reduces ethanol induced phospholipase A2 activity in synaptosomal preparations from mice.

The adaptation (tolerance) to chronic EtOH exposure was explained by the development of resistance to the disordering of the membrane phospholipids (PL). This phenomenon may be associated with changes in enzymes such as phospholipase A2 (PLA2) that govern PL metabolism. The data presented here, using the mouse inhalation model, supports and confirms previously reported findings that chronic exposure to EtOH substantially increased PLA2 activity in synaptosomal preparations from rat brain. We have previously reported that pretreatment with ganglioside GM1 reduced the intoxicating effect of EtOH in mice. The present study indicates that GM1 pretreatment both in vivo and in vitro reduced the EtOH-induced activation of PLA2 in synaptosomal preparations. Thus GM1 may exert its neuroprotective effects by influencing deacylation/reacylation of membrane phospholipids.

Animals↗
PubMed1994

Sequences of four splits of HLA-A10 group. Implications for serologic cross-reactivities and their evolution.

Nucleotide sequences of alleles encoding four serologically defined splits of the HLA-A10 group, A26.1, A26.3, A26.4, and A10SA, were determined. It was confirmed that the alleles coding for A26.1 and A26.3 are identical with A*2602 and A*2601, respectively. On the other hand, alleles for A26.4 and A10SA are thus far undescribed. A26.4 (A*2603) was different from the other A26 splits at three positions: 74 histidine, 76 valine, and 77 aspartate. A10SA (A*2604) was different from A26.3 (A*2601) by a single substitution of arginine by leucine at position 163. A comparison of amino acid sequences of HLA-A10 cross-reacting antigens revealed that all of the A10 group antigens share specific amino acids: 142 isoleucine, 144 glutamine, 145 arginine, 149 threonine, and 152 glutamate. Moreover, A26.1, A26.3, A10SA, and A43 share 76 alanine and 77 asparagine, which is consistent with the reported serologic cross-reactivity. The close relationship between the alleles for the A10 cross-reacting group was supported by a phylogenetic tree analysis for the HLA-A alleles.

Alleles↗
PubMed1994

Modulation of hepatocyte growth factor gene expression by estrogen in mouse ovary.

Hepatocyte growth factor (HGF) is expressed in a variety of tissues and cell types under normal conditions and in response to various stimuli such as tissue injury. In the present study, we demonstrate that the transcription of the HGF gene is stimulated by estrogen in mouse ovary. A single injection of 17 beta-estradiol results in a dramatic and transient elevation of the levels of mouse HGF mRNA. Sequence analysis has found that two putative estrogen responsive elements (ERE) reside at -872 in the 5'-flanking region and at +511 in the first intron, respectively, of the mouse HGF gene. To test whether these ERE elements are responsible for estrogen induction of HGF gene expression, chimeric plasmids containing variable regions of the 5'-flanking sequence of HGF gene and the coding region for chloramphenicol acetyltransferase (CAT) gene were transiently transfected into both human endometrial carcinoma RL 95-2 cells and mouse fibroblast NIH 3T3 cells to assess hormone responsiveness. Transfection results indicate that the ERE elements of the mouse HGF gene can confer estrogen action to either homologous or heterologous promoters. Nuclear protein extracts either from RL95-2 cells transfected with the estrogen receptor expression vector or from mouse liver bound in vitro to ERE elements specifically, as shown by band shift assay. Therefore, our results demonstrate that the HGF gene is transcriptionally regulated by estrogen in mouse ovary; and such regulation is mediated via a direct interaction of the estrogen receptor complex with cis-acting ERE elements identified in the mouse HGF gene.

3T3 Cells↗
PubMed1994

Molten globular characteristics of the native state of apomyoglobin.

Apomyoglobin, myoglobin lacking the haem group, is a natural intermediate in biosynthesis of myoglobin, and has some structural features in common with the haem-containing native state. Unfolding or refolding studies of apomyoglobin have identified a molten globule intermediate at acid pH. We show here that both the native state of apomyoglobin and the molten globule intermediate have highly plastic structures. Substitution of single amino acids on the surface or in the interior of helices in the native protein produce dramatic changes in the helix content and tryptophan emission of apomyoglobin at neutral and acidic pH. The signals from the intermediate and native apomyoglobin correlate closely suggesting that apomyoglobin itself has a molten globule-like character, its structure representing a population of interconverting substates rather than a fixed conformation.

Animals↗
PubMed1994

Localization of pituitary adenylate cyclase-activating polypeptide (PACAP) in the hypothalamus-pituitary system in rats: light and electron microscopic immunocytochemical studies.

The localization of pituitary adenylate cyclase-activating polypeptide (PACAP) in the hypothalamus-pituitary system in rats was examined in light and electron microscopic immunocytochemistry using a specific antiserum to synthetic PACAP 1-38 (R0831). In light microscopic study, intensely PACAP-immunostained perikarya were observed in the supraoptic and paraventricular magnocellular nucleus in the hypothalamus. In the median eminence, many immunoreactive nerve fibers were observed in the internal layer, but a few immunoreactive terminals were noticed in the external layer. In the pituitary gland, numerous immunoreactive nerve fibers were observed in the posterior lobe. In the intermediate lobe, moderately immunostained cells were observed, but in the anterior lobe no immunostained cells were noticed. In electron microscopic study, PACAP-immunoreactivity was examined by avidin-biotin peroxidase complex method. In the perikarya of the supraoptic and paraventricular magnocellular nucleus, DAB-reaction products were distributed diffusely in the cytoplasmic matrix, frequently attaching to the rough-surfaced endoplasmic reticulum. In the nerve terminals of the posterior lobe, reaction products were observed among the secretory granules, but sometimes upon them. In the cells of the intermediate lobe, reaction products were also distributed in the cytoplasmic matrix.

Animals↗
PubMed1994

The opaH locus of Neisseria gonorrhoeae MS11A is involved in epithelial cell invasion.

In order to produce a successful infection, Neisseria gonorrhoeae (GC) must attach to and invade mucosal epithelial cells. To identify GC gene products involved in this early interaction with host cells we constructed a gene bank derived from a clinical isolate of GC, and isolated a clone which had the capacity to adhere to the human endometrial adenocarcinoma tissue-culture line HEC-1-B. The cloned sequence was identified as a member of the opa gene family whose protein products have been associated with virulence. The GC chromosome contains numerous variant opa genes which, in MS11, are designated opaA-K. Previous work showed that expression of opaC confers a highly invasive phenotype upon strain MS11. When our cloned opa gene was mutated and returned to the GC MS11A chromosome by transformation and homologous recombination, we isolated one transformant that was significantly reduced in its invasive capacity. The locus mutated in this transformant was identified as opaH. Our results indicate that invasiveness of GC for human epithelial cells can be determined by more than one opa gene in strain MS11A.

Amino Acid Sequence↗
PubMed1994

Sequence analysis of serological HLA-A11 split antigens, A11.1 and A11.2.

HLA-A11 has two serologically-defined splits, A11.1 and A11.2, and two alleles coding for HLA-A11, A*1101 and A*1102, have been published so far. In order to understand the relationship between the serological subtypes and the amino acid sequences, we have sequenced the alleles coding for A11.1 and A11.2. The results demonstrated that A11.1 split antigen is encoded by A*1101 and A11.2 split antigen is encoded by A*1102. Moreover, we obtained the sequences of exons 1, 5, 6, 7, and 8 of A*1102, which were not reported previously. In addition, we could distinguish A*1101 from A*1102 using a PCR-SSCP method, confirming that A11.1 carried by different HLA haplotypes has the same sequence.

Amino Acid Sequence↗
PubMed1994

Discrimination of human HLA-DRB1 alleles by PCR-SSCP (single-strand conformation polymorphism) method.

A single-strand conformation polymorphism (PCR-SSCP) method has been adopted for discrimination of human HLA-DRB1 alleles. This method enabled the detection of DNA polymorphisms including point mutations at a variety of positions in the DNA fragments of the HLA-DRB1 gene. A total of 27 HLA-DRB1 alleles from 172 healthy donors were analysed using a combination of PCR-SSCP with group-specific amplifications. Application of a small amount of amplified and denatured DNA to non-denaturing electrophoresis followed by silver staining resulted in distinct banding patterns. Samples possessing a single allele in each amplification group showed two-band patterns which correspond to the sense and antisense strands, while heterozygotes in the same group or a mixture of two single-type samples showed four-band patterns. All of the analysed alleles were discriminated in each DRB1 group. The method described here may be somewhat complicated for routine typing of HLA-DRB1 alleles. However, it is useful in the screening of "new' alleles as well as the donor-recipient molecular matching of HLA class II genes for various purposes, e.g. selection of bone marrow transplant donors.

Alleles↗
PubMed1994

Temporal changes of pharmacokinetics, nephrotoxicity, and subcellular distribution of tobramycin in rats.

The present study was designed to determine the temporal changes in tobramycin nephrotoxicity during the dark and the light periods of the day and to look for the mechanisms of such changes. Female Sprague-Dawley rats (9 to 11 weeks old) were housed in a 14-h-light-10-h-dark cycle (lights on 0600 to 2000 h). A bolus of tobramycin (60 mg/kg of body weight) was intravenously injected into a first group of 15 rats, at either 1400 or 0200 h. Six blood samples were taken from each rat, 30 to 210 min after the bolus injection. The total clearance of the drug was reduced during the rest period (1400 h) of rats compared with the activity period (0200 h) (P = 0.0007). Another group of 99 rats was given intraperitoneally a single dose of tobramycin (40 mg/kg), and renal cortices were collected 2 to 222 h after injection. The cortical drug levels were always higher in animals injected at 1400 h than in those injected at 0200 h. A last group of 32 rats was used in the studies of tobramycin (30 mg/kg/day, once daily for 10 days, intraperitoneally) nephrotoxicity and subcellular distribution. Weight gain in the rats receiving tobramycin (both 1400 and 0200 h) was significantly (P = 0.028) less than that in the controls. Nephrotoxicity, indicated by the incorporation of [3H]thymidine into cortical DNA and urinary excretion of N-acetyl-beta-D-glucosaminidase, was significantly higher in animals treated at 1400 h than in those treated at 0200 h. No difference in the subcellular distribution of tobramycin was observed. The data indicate that the reduction in the clearance of tobramycin during the rest period is in part responsible for the higher nephrotoxicity in rats.

Acetylglucosamine↗
PubMed1994

Daptomycin may attenuate experimental tobramycin nephrotoxicity by electrostatic complexation to tobramycin.

The lipopeptidic antibiotic daptomycin is reported to reduce experimental tobramycin nephrotoxicity (D. Beauchamp, M. Pellerin, P. Gourde, M. Pettigrew and M. G. Bergeron, Antimicrob. Agents Chemother. 34:139-147, 1990; C. A. Wood, H. C. Finkbeiner, S. J. Kohlhepp, P. W. Kohnen, and D. C. Gilbert, Antimicrob. Agents Chemother. 33:1280-1285, 1989). In an attempt to explain these results, the in vivo and in vitro interactions between daptomycin and tobramycin were studied. Tobramycin alone and preincubated with negatively charged phospholipid bilayers (liposomes) was dialyzed against increasing concentrations of daptomycin in buffer at pH 5.4. A significant drop in the concentration of tobramycin was observed when daptomycin was added to the opposite half cells. Furthermore, daptomycin induced a concentration-dependent release of lipid-bound tobramycin. Gold labeling experiments showed that daptomycin could be incorporated into phospholipid layers. Female Sprague-Dawley rats were treated with daptomycin alone, with tobramycin alone, or with the combination over 2 to 10 days. Levels of daptomycin and tobramycin in serum were similar in all groups. The levels of tobramycin in the renal cortex increased significantly with time and, on day 10, reached values of 654 +/- 122 and 844 +/- 298 micrograms/g of tissue (mean +/- standard deviation; not significant) in animals treated with tobramycin and the combination of daptomycin-tobramycin, respectively. No significant difference was observed in the levels of tobramycin in the kidneys between animals treated with tobramycin or the daptomycin-tobramycin combination at any time. By contrast, daptomycin levels were significantly higher in the renal cortexes of animals treated with daptomycin-tobramycin in comparison with those in the renal cortexes of animals treated with daptomycin alone on days 6,8, and 10 (P < 0.01). For immunogold labeling studies, animals were killed 4 h after a single injection of daptomycin alone or daptomycin in combination with tobramycin. Daptomycin was found throughout the matrixes of the lysosomes of proximal tubular cells of animals treated with daptomycin alone. In animals treated with the combination of daptomycin and tobramycin, daptomycin was associated with intralysosomal myeloid bodies. Our results suggest that daptomycin might attenuate experimental aminoglycoside nephrotoxicity by interacting with the aminoglycoside, perhaps electrostatically, and thereby protecting intracellular targets of toxicity.

Animals↗
PubMed1994

Identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse hepatocyte growth factor gene.

Hepatocyte growth factor (HGF), a cytokine with multiple functions, exhibits cell-type-specific as well as cytokine- and steroid hormone-regulated expression. The HGF gene is known to be expressed predominately in mesenchymal but not in epithelial cells. In this study, we report the identification of a cell-type-specific transcriptional repressor in the promoter region of the mouse HGF gene, which is evidently responsible for the suppression of HGF expression in epithelial cells. Gel mobility shift assays and DNase I footprinting studies revealed that a 27-bp element (-16 to +11) around the transcription initiation site is responsible for the binding of a nuclear protein which is present in epithelial but not in mesenchymally derived cells. Further analysis of the binding activity of the DNA region with nuclear protein revealed that an approximately 19-bp sequence containing a unique palindromic structure (5'-AACCGACCGGTT-3') overlapped by a CAP box is essential for binding. Substitution of a single base (the contact site) within this region by site-directed mutagenesis resulted in total abrogation of the binding of the nuclear protein and a concomitant increase in the transcriptional activity of various lengths of HGF-chloramphenicol acetyltransferase fused genes when transfected into the epithelial cell line RL95-2 but not the mesenchymal cell line NIH 3T3. Southwestern (DNA-protein) analyses revealed that the nuclear protein which binds to this repressor element is a single polypeptide of approximately 70 kDa. Analysis of the nuclear extract prepared from regenerating mouse liver at various times after two-thirds partial hepatectomy by gel mobility shift assay revealed a substantial reduction (more than 75% within 3 h) in the binding of the repressor to its cognate binding site. Our results suggest that a cis-acting transcriptional repressor in the promoter region of the mouse HGF gene is involved in cell-type-specific regulation through binding to its cognate trans-acting protein which exists in epithelial cells but is absent in fibroblast cells.

Animals↗
PubMed1994

Induction of the rat prodynorphin gene through Gs-coupled receptors may involve phosphorylation-dependent derepression and activation.

Prodynorphin transcription is activated via Gs-coupled receptors through a cyclic AMP (cAMP)-dependent pathway. Four cAMP response elements (CREs) are present within the rat prodynorphin (RD) control region, and all four CREs appear to function in RD regulation. Three CREs located upstream between -1860 and -1504 are critical for receptor-responsive activity, but their function is distance dependent unless they act together with a fourth CRE found in exon 1. Regulation of RD also appears to involve multiple CRE-binding proteins. Both CRE-binding protein (CREB) and activator protein 1 (AP-1) can regulate RD, but their effects are in opposite directions; CREB represses and AP-1 activates RD. CREB-induced repression and AP-1 activation require distinct elements within the control region, but their binding and functions overlap at CRE-3. While CREB repression is dependent on CRE-3, AP-1 activation (and cAMP induction) of RD requires additional CREs (CRE-1, -2, and -4). CREB repression blocks AP-1 activation in unstimulated cells. However, phosphorylation relieves CREB-induced repression and enhances AP-1 activation. Gs-coupled receptor activation of RD may require phosphorylation-dependent derepression and activation steps.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1994

Vascular responsiveness to nitric oxide synthesis inhibition in hypertensive rats.

We contrasted in normotensive and hypertensive rats the effect of inhibition of nitric oxide synthesis on isometric tension development by aortic rings bathed in Krebs' bicarbonate buffer. NG-Nitro-L-arginine methyl ester (L-NAME) (3 x 10(-4) mol/L) increased tension (82 +/- 11% of the response to 120 mmol/L potassium chloride) in rings of thoracic aorta taken from hypertensive rats 7 to 14 days after aortic coarctation, whereas rings of abdominal aorta from below the coarctation were unresponsive, as were rings of thoracic aorta from rats with deoxycorticosterone-salt-induced hypertension and from the corresponding normotensive controls of either model of hypertension. The contractile response to L-NAME in aortic rings of rats with aortic coarctation was reversed by L-arginine (1 mmol/L), attenuated by removal of the endothelium, and blunted by the protein kinase C inhibitor staurosporine but was unaffected by inhibition of cyclooxygenase, scavengers of superoxide anion, or blockade of receptors for angiotensin, norepinephrine, serotonin, or endothelin. In additional experiments we contrasted the effect of L-NAME (10 mg/kg IV) on the blood pressure of sham-operated rats and rats with aortic coarctation after pretreatment of animals in both groups with DuP 753 (30 mg/kg IV) to achieve blood pressure equalization. The pressor response to L-NAME was twofold greater in rats with aortic coarctation than in sham-operated controls. That pressor and aortic constrictor responsiveness to L-NAME are increased after aortic coarctation suggests that a mechanism of vasodilation, mediated by nitric oxide, is preferentially manifested in rats with aortic coarctation-induced hypertension.

Animals↗
PubMed1994

Expression of prostaglandin H2-mediated mechanism of vascular contraction in hypertensive rats. Relation to lipoxygenase and prostacyclin synthase activities.

We tested the hypothesis that a prostanoid-mediated mechanism of vascular contraction is expressed in rats with aortic coarctation-induced hypertension. Rings of descending thoracic aorta taken from normotensive and hypertensive rats were contrasted in terms of constrictor responsiveness to arachidonic acid (AA), AA-induced release of eicosanoids, and ability to convert exogenous prostaglandin (PG) H2 to PGI2. AA (10(-8) to 10(-5) mol/L) increased isometric tension in aortic rings (bathed in Krebs' bicarbonate buffer) of hypertensive but not normotensive rats. AA (10(-5) mol/L) also elicited the release of PGI2, PGE2, thromboxane (TX) A2, and monohydroxyeicosatetraenoic acids (HETEs); this release from the aortic rings of hypertensive rats exceeded the corresponding release from the aortic rings of normotensive rats. However, the rate of conversion of exogenous PGH2 to PGI2 by aortic rings of hypertensive rats was < 50% the rate of conversion by aortic rings of normotensive rats. The constrictor effect of AA in aortic rings of hypertensive rats was abolished by an inhibitor of cyclooxygenase (indomethacin, 10 mumol/L) and a blocker of TXA2-PGH2 receptors (SQ29548, 1 mumol/L) but was not affected by an inhibitor of TXA2 synthesis (CGS13080, 10 mumol/L), suggesting mediation by PGH2. The lipoxygenase inhibitor baicalein (75 mumol/L) also attenuated the constrictor effect of AA in aortic rings of hypertensive rats while decreasing the associated release of HETEs and correcting the impairment in the conversion of PGH2 to PGI2.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

[The effect of Baji Zibugao on the serum levels of endocrines in thyroidectomized (yang deficiency) rabbits].

In order to study the effect of Baji Zibugao (BJZBG, a medicinal plaster mainly consisting of Radix Morindae Officinalis) on the endocrine functions of hypothyroid rabbits, we determined the serum levels of thyroxine (T4), triiodothyronine (T3), cAMP, cGMP and corticosterone in three groups of rabbits: total thyroidectomized and untreated (group I), total thyroidectomized and treated with BJZBG (group II) and controls (group III). The results showed: (1) The serum level of T4 in group I and II after operation was significantly lower than that before operation (P < 0.005), and the serum level of T3 in group I was also lower than that before operation (P < 0.02), but the change of T3 in group II after operation was not significant (P > 0.05); (2) The serum cAMP level in group I after operation decreased and the cGMP level increased (P < 0.025), but the changes of cAMP and cGMP level in group II after operation were not significant (P > 0.05), (3) The change of serum corticosterone level in group I or II after operation was not remarkable (P > 0.05).

Animals↗