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Biomedical subjects

J Tan

Publications and source records attributed to J Tan.

At least 163 records · Page 9Linked to original sources
PubMed1998

The pH dependent amelogenin solubility and its biological significance.

Amelogenins are a group of extracellular enamel matrix proteins which are believed to be involved in the regulation of the size and habit of enamel crystals. The aim of this study was to compare the solubility properties of several amelogenins in various pH (4.0-9.0) solutions with an ionic strength (IS) of 0.15 M using the Micro BCA protein assay at 25 degrees C or 37 degrees C. The solubility of the recombinant amelogenin rM179 was lowest (0.7 mg/ml) close to its isoelectric point and it increased below and above this point. The solubility of the recombinant amelogenin rM166 remained almost the same (1-2 mg/ml) as the pH rose from 6.0 to 9.0 and it increased as the solution became more acidic. Synthetic "tyrosine-rich amelogenin polypeptide" (TRAP) was extremely insoluble (<0.2 mg/ml) in the pH range studied while synthetic "leucine-rich amelogenin polypeptide" (LRAP) was readily soluble (>3.3 mg/ml). The native porcine amelogenin with apparent molecular weight 25 kDa shared similar solubility behavior to rM179. The porcine 23 kDa amelogenin was only sparingly soluble (0.3-0.8 mg/ml) over a wide range of pH. Interestingly, the porcine 20 kDa amelogenin was remarkably soluble in the pH range of 4.0 to 6.0 (approximately 12 mg/ml), but the solubility dropped strikingly to only approximately 0.2 mg/ml at pH larger than approximately 7.0. The strong dependence of amelogenin solubility on solution pH may be involved in the regulation of aggregation, enzymatic degradation and the binding properties of amelogenins, thus playing an important role in enamel biomineralization.

Amelogenin↗
PubMed1998

Does amelogenin nanosphere assembly proceed through intermediary-sized structures?

We have proposed that these nanosphere structures are functionally involved in the organization and control of initial enamel biomineralization at the ultrastructural level. Based on the observed nanosphere hydrodynamic radii (18-20 nm diameter) computation suggests these structures to be compounded of some 100 amelogenin monomers, raising the question as to the possible molecular mechanism for the assembly of such structures? Based on recent dynamic light scattering experiments using the recombinant murine amelogenin M179, and employing a newer size distribution algorithm we now report that the size distribution data for M179 are better described by a bimodal distribution model, than the monomodal distribution as previously described. We suggest that amelogenin nanosphere assembly proceeds through intermediate structures (perhaps represented in vivo by "stippled material") of some 4-5 nm hydrodynamic radius, and computed to comprise 4-6 amelogenin monomers. We suggest that such intermediary, sub-unit structures, assemble through inter-molecular hydrophobic interactions to generate the 20 nm diameter nanospheres observed by TEM in the secretory stage enamel matrix.

Amelogenin↗
PubMed1998

Effect of apatite crystals on the activity of amelogenin degrading enzymes in vitro.

The objective of the present study was to determine the effect of apatite crystals on the activity of amelogenin degrading enzymes in vitro. Current experimental data, together with previous reports support the view that among the different proteinases present in the enamel extracellular matrix, serine proteinase(s) are responsible for the massive degradation of amelogenins during the maturation stage. For our in-vitro experiments we used the recombinant amelogenin M179 as substrate and a "65%-satd. (NH4)2SO4" fraction of enamel proteins as well as chymotrypsin as sources for serine-proteinase activity. We report preliminary experiments of amelogenin proteolysis in the presence of apatite crystals resulting in a different proteolysis pattern when compared to amelogenin proteolysis without apatite crystals. Quantitative analysis of the HPLC peaks corresponding to the proteolysis products indicates that the presence of apatite crystals in the proteolysis solution inhibits the ability of the serine-proteinases to degrade amelogenin. The present observations support the hypothesis that amelogenin degradation correlates with apatite crystal growth during enamel maturation.

Amelogenin↗
PubMed1998

[Effect of manganese on the growth and development of rat offspring].

Effects of Manganese exposure to pregnant rats on the growth and development of their offsprings were as follows: (1) the gain of body weight and brain weight in the high dose Mn-exposed offspring was significantly lower but the ratio of brain to body weight was significantly higher; (2) in Morris Water Maze Test, the average latency to find the hidden platform in the high dose Mn-exposed offsprings was obviously reduced during the first 5 days. But on the non-platform test day, a much longer length of swimming in the quadrant in which the hidden platform was located previously, although no difference was found for the total distance between them; (3) the immunoreactivity of glial fibrillary acid protein and the average density of its products in hippocampus of both the low and high dose Mn-exposed groups, especially of the high dose one, was significantly higher than that of the control group.

Animals↗
PubMed1998

[Changes of cerebral blood flow during hypoxicischemic encephalopathy in newborn pigs].

This study was designed to explore the change of cerebral blood flow during hypoxic-ischemic encephalopathy (HIE). Sixteen newborn pigs were devided into four groups: the normal control, 15 minutes after HIE, 30 minutes after HIE and 60 minutes after HIE. The shapes of the cerebral blood vessels were obsessed by the prepared Chinese ink irrigation and the width and volume fraction of capillary were tested and analyzed by stereographic method respectively. The results showed the small blood vessels were interrupted with the passage of time. At the time of 60 minutes after HIE, capilaries almost disappeared from view, only a few ends of blood vessels in the sheap of a broken tree were seen. The width of capillaries and small veins became more and more narrow as time went on. The percentages of capillary volume fraction and small vein volume fraction became smaller and smaller (P < 0.05). These demonstrate that the fall of cerebral blood flow plays an important role in the development of HIE.

Animals↗
PubMed1998

[An endometrium morphometry study on ovariectomized rats subjected to nilestriol and estradiol replalcement therapies].

This study was designed to evaluate the effect of estrogen on rat endometrium and compare the results of Nilestriol and Estradiol replacement therapies for preventing osteoporosis in ovariectomized rats. Forty 4-month old SD female rats were randomly divided into four groups, namely sham operation, bilateral ovariectomy, ovariectomy plus supplementary ethinyl estradiol (0.2 microgram/100 g B. W. qd x 5), and ovariectomy plus supplementary Nilestriol (0.15 mg/100 g B. W. once a week). Computerized image analyzer was used to evaluate the endomitrial pathological changes 10 weeks later. The results showed an atrophied endometrium in ovariectomized group, a slightly proliferative endometrium in Nilestriol treated group, and a markedly proliferative endometrium with local atypical hyperplasia in estradiol treated group. The difference between group 3 and group 4 in morphometry was significant (P < 0.5). These suggest the relative safety of Nilestriol replacement therapy for preventing menopausal osteoporosis.

Animals↗
PubMed1998

[DNA typing for HLA-A, B antigens by polymerase chain reaction with sequence-specific primers and clinical application].

OBJECTIVE: To establish DNA typing for HLA-A, B antigens in Chinese by polymerase chain reaction with sequence-specific primers (PCR-SSP). METHODS: DNA samples were obtained from 178 unrelated donors and 167 kidney recipients. An additional panel of 62 standard DNAs that were typed by UCLA tissue typing lab in USA. A rapid genotyping for HLA-I class (A, B antigens) by PCR-SSP was set up by designed and synthesized 81 specific primers and 1 pair of internal control primer, combining in 61 one-step reactions (20 PCR reactions for A alleles, 41 PCR reactions for B alleles). RESULTS: HLA-A, B alleles were successfully typed in 345 clinical samples and 62 standard DNAs by PCR-SSP technique. No false positive or false negative typing results were obtained. Reproducibility was 100% in 40 samples. The overall time of DNA typing was 5 hours. The typing results were consistent with those of UCLA tissue typing lab. Nineteen alleles of HLA-A and 41 HLA-B alleles were accurately distinguished. Thirteen HLA-A alleles and thirty-two HLA-B alleles in Chinese were practically typed. CONCLUSION: DNA typing for HLA-I class (A, B antigens) by PCR-SSP has proved to be a technique of high-resolution, high-specificity, well-reproducibility, and more suitable for clinical application than serology.

Adolescent↗
PubMed1998

[A comparative study of serological, monoclonal antibody and DNA typing in identifying HLA-A].

OBJECTIVE: A double-blind study was carried out to evaluate the accuracy and reliability of PCR-SSP assay in comparison with serology and monoclonal antibody(mAb) typing in identifying HLA-A alleles in Southern Chinese population. METHODS: A total of 296 samples were entered into the study, including 143 unrelated kidney donors and 153 recipients. HLA-A typing was performed by standard two-stage microlymphocytotoxicity assay, one-step mAb typing and PCR-SSP typing. RESULTS: All samples were successfully typed by PCR-SSP. Reproducibility was 100%. The results were confirmed by a panel of standard DNAs and a double-blind typing of UCLA tissue typing lab. However, mAb typing(for Asian) in 149 samples showed 2.7% misassignment including 1 antigen being incorrectly interperted and 3 of 26 "blanks" turning out to be definable alleles by DNA typing. Serological discrepancy rate was 15.6% in 147 samples consisting of 8 antigens being incorrectly interpreted, 13 "blanks" turning out to be definable alleles and 2 heterozygotes turning out to be homozygotes by DNA typing. CONCLUSION: HLA-A typing by PCR-SSP proved to be a rapid and accurate technique, suitable for clinical application with a greater precision than serology. In large scale screening, mAb typing (for Asian) is recommended. Antigens of "blanks" or "difficult" by serology or mAb typing should be retyped by DNA typing.

Alleles↗
PubMed1998

[Effect of different processing conditions on content of myrisiticin, volatile oil and fatty lipid in semen Myristicae].

The effect of different processing conditions on contents of myrisiticin, volatile oil and fatty lipid in Semen Myristicae was studied by orthogonal design. The result shows that these processing conditions could not influence the contents of myrisiticin, volatile oil and fatty lipid in the processed products of Semen Myristicae, suggesting that processing does not necessarily lower toxicity.

Allylbenzene Derivatives↗
PubMed1998

[Computer aided photocclusion analysis of traumatic occlusion].

OBJECTIVE: This study was designed to analyse traumatic occlusion quantitatively. METHODS: A photocclusion method using computer image processing technique is described, the processing software provide the occlusal contact area, contact point numbers, contact force, maximum stress, and average stress distribution of all teeth by tables and figures. RESULTS: (1) The traumatic contact area was larger and contact force was greater than that of the normal occlusal contact. (2) There was an irregularity force distribution from molars to incisal area. (3) The symmetrical distribution of contact forces and contact areas were destroyed. CONCLUSION: Computer aided-photocclusion method can be used to diagnose traumatic occlusion.

Dental Occlusion, Traumatic↗
PubMed1998

[Facial soft tissue features analysis of normal Han race adults in Guangdong Province using computer-assisted-photogrammetric-system].

Facial soft tissue profile features of 150 normal native adults of Guangdong Province were analysed using computer-assisted-photogrammetric-system, which contained parameters written by polar coordinate. The results indicated that normal native adults of Guangdong Han race showed sex and region difference in features of facial profile soft tissue, and those parameters written by polar coordinate were helpful in the further study and clinical therapy.

Adult↗
PubMed1998

In vivo MR spectroscopy of human dementia.

Nuclear MR spectroscopy in low and medium magnetic fields yields well-resolved natural abundance proton and decoupled phosphorus spectra from small (1-10 mL) volumes of brain in vivo in minutes. With this tool, neurochemical research has advanced through identification and noninvasve assay of a specific neuronal-cf2Ncf1-acetylaspartate, glial (cf2myocf1-inositol)-markers, energetics and osmolutes, and neurotransmitters (glutamate, GABA). From these simple measurements, several dozen disease states are recognized, including birth injury, and white matter and Alzheimer disease. Together, these tools are having a major impact on neuroscience and clinical medicine.

Alzheimer Disease↗
PubMed1997

Safety-modified episomal vectors for human gene therapy.

The effectiveness of ongoing gene therapy trials may be limited by the expression characteristics of viral and plasmid-based vectors. To enhance levels of heterologous gene expression, we have developed a safety-modified episomal expression vector that replicates extrachromosomally in human cells. This vector system employs a simian virus 40 (SV40) large T antigen mutant (107/402-T) that is deficient in binding to human tumor suppressor gene products, including p53, retinoblastoma, and p107, yet retains replication competence. These SV40-based episomes replicate to thousands of copies by 2-4 days after gene transfer in multiple types of human cell lines, with lower activity in hamster cells, and no detectable activity in dog, rat, and murine cell lines. Importantly, 107/402-T has enhanced replication activity compared with wild-type T antigen; this finding may be due, in part, to the inability of p53 and retinoblastoma to inactivate 107/402-T function. We demonstrate that the level and duration of 107/402-T expression regulates the observed episomal copy number per cell. Compared with standard plasmid constructs, episomes encoding 107/402-T yield approximately 10- to 100-fold enhanced levels of gene expression in unselected populations of transient transfectants. To determine if 107/402-T-based episomes replicate extrachromosomally in vivo, tumor explants in nude mice were directly injected with liposome/DNA complexes. Using a PCR-based assay, we demonstrate that SV40-based episomes replicate in human cells after direct in vivo gene transfer. These data suggest that safety-modified SV40-based episomes will be effective for cancer gene therapy because high level expression of therapeutic genes in transient transfectants should yield enhanced tumor elimination.

Animals↗
PubMed1997

Suppression of substance P biosynthesis in sensory neurons of dorsal root ganglion by prodrug esters of potent peptidylglycine alpha-amidating monooxygenase inhibitors.

Substance P as well as many other neuropeptides are synthesized as glycine-extended precursors and converted to the biologically active C-terminal amides by posttranslational modification. The final step of posttranslational processing is catalyzed by peptidylglycine alpha-amidating monooxygenase (PAM). In a previous study, N-substituted homocysteine analogs were found to be potent inhibitors of PAM partially purified from conditioned medium of cultured rat medullary thyroid carcinoma CA-77 cells. These compounds, however, were only modest inhibitors of substance P production in cultured dorsal root ganglion cells, possibly because of poor cell penetration. Several ester derivatives of hydrocinnamoyl-phenylalanyl-homocysteine, one of the most potent PAM inhibitors, were prepared to increase the intracellular accessibility of these compounds. Hydrocinnamoyl-phenylalanyl-(S-benzoyl-homocysteine) benzyl ester was identified as the most potent compound, inhibiting substance P biosynthesis in dorsal root ganglion cells with an IC50 of 2 microM. Inhibition of PAM resulted in a concomitant increase in the glycine-extended substance p (substance P-Gly) precursor peptide. In the presence of 3 microM benzyl ester derivative, the intracellular substance P-Gly level was 2.4-fold higher while the substance P level was 2.1-fold lower than the corresponding peptides in control cells. These results suggest that PAM inhibition represents an effective method for suppression of substance P biosynthesis and, therefore, may have therapeutic utility in conditions associated with elevated substance P levels. Furthermore, PAM inhibition may also prove useful in decreasing other amidated peptides.

Animals↗
PubMed1997

Characterization of interleukin-10 receptor expression on B-cell chronic lymphocytic leukemia cells.

B-cell chronic lymphocytic leukemia (B-CLL) cells accumulate in vivo in the G0/G1 phase of the cell cycle, suggesting that their malignant expansion is due, at least in part, to a delay in cell death. However, the cellular or molecular factors responsible for a delay in B-CLL cell death are unknown. B-CLL cells do express receptors for interferon-alpha (IFN-alpha) and IFN-gamma, and activation of both has been shown to promote B-CLL survival in vitro by preventing apoptosis. The interleukin-10 (IL-10) receptor is another member of the IFN receptor family, but its ligand, IL-10, has been reported to induce apoptosis in B-CLL cells. In the current study, we undertook a biochemical analysis of IL-10 receptor expression on freshly isolated B-CLL cells and characterized the functional responsiveness of IL-10 binding to its constitutively expressed receptor. We show that B-CLL cells bind IL-10 with significant specificity and express between 47 and 127 IL-10 receptor sites per cell, with a dissociation constant in the range of 168 to 426 x 10(-12) mol/L. Ligand binding and activation of the IL-10 receptor expressed on B-CLL cells results in the phosphorylation of signal transducer and activator of transcription 1 (STAT1) and STAT3 proteins. This pattern of STAT protein phosphorylation is identical to IL-10 receptor activation on normal cells and similar to IFN-alpha (STAT1 and STAT3) and IFN-gamma (STAT1) receptor activation in CLL. Further, in consecutive samples of fresh blood obtained from patients with B-CLL cells, the addition of IL-10 inhibited B-CLL proliferation, enhanced B-CLL differentiation, but did not induce apoptosis. Indeed, IL-10, like IFN-gamma, was able to significantly reduce the amount of B-CLL cell death caused by hydrocortisone-induced apoptosis. We conclude that cytokines, which signal through the interferon family of receptors, have comparable functional effects on B-CLL cells.

B-Lymphocytes↗
PubMed1997

Human papillomavirus type 16 DNA in esophageal carcinomas from Alaska Natives.

The possible etiological role of human papillomavirus (HPV) in esophageal carcinogenesis was evaluated in Alaska Natives in whom the incidence of esophageal cancer is 1.3 and 3.8 times higher than in US Caucasian men and women, respectively. Fixed paraffin-embedded esophageal tissues from 32 cases of squamous-cell carcinoma (SCC) and 3 cases of adenocarcinoma (AC) diagnosed between 1957 and 1988 were analyzed by polymerase chain reaction (PCR) and in situ hybridization for HPV DNA sequences. Detection of the human beta-globin gene by PCR was used as a control for sufficiency of DNA and its potential for amplification in the tissue samples. Twenty-five of the tumor tissues were considered adequate for PCR analyses; HPV DNA was detected in 10 of 22 SCCs and was not found in 3 ACs. Seven of the 10 HPV-positive tissues contained sequences from the E6 gene of HPV type 16. Koilocytosis, an epithelial change consistent with HPV infection, was found in 80% of the esophageal squamous-cell tumors with HPV DNA and in 75% of those without HPV DNA. The detection of amplifiable cellular DNA was related to recentness of diagnosis; however, the detection of HPV DNA within amplifiable specimens was not related to recentness of diagnosis. A 413-bp sequence from the L1 open reading frame of HPV 16 from esophageal tissue of 2 patients was identical to sequences previously identified in cervical cells from other Alaska Natives. Our results provide molecular evidence of HPV infection, especially type 16, in archival esophageal cancer tissues from 45% of those patients whose specimens contain adequate DNA for PCR analysis.

Adenocarcinoma↗
PubMed1997

The use of the Internet in dentistry.

With internet connectivity, a new horizon of scientific co-operation and collaboration at global level has been opened. Anyone can have easy access to information on not only public health and hygiene matters, but also on more esoteric aspects of dental practice. This article points out the use of the internet in dentistry.

Computer Communication Networks↗