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Biomedical subjects

M Lin

Publications and source records attributed to M Lin.

At least 199 records · Page 11Linked to original sources
PubMed1997

Posttesticular development of spermatozoa of the tammar wallaby (Macropus eugenii).

Tammar wallaby spermatozoa undergo maturation during transit through the epididymis. This maturation differs from that seen in eutherian mammals because in addition to biochemical and functional maturation there are also major changes in morphology, in particular formation of the condensed acrosome and reorientation of the sperm head and tail. Of spermatozoa released from the testes, 83% had a large immature acrosome. By the time spermatozoa reached the proximal cauda epididymis 100% of sperm had condensed acrosomes. Similarly 86% of testicular spermatozoa had immature thumb tack or T shape head-tail orientation while only 2% retained this immature morphology in the corpus epididymis. This maturation is very similar to that reported for the common brush tail possum, Trichosurus vulpecula. However, morphological maturation occurred earlier in epididymal transit in the tammar wallaby. By the time spermatozoa had reached the proximal cauda epididymis no spermatozoa had an immature acrosome and thumbtack orientation. Associated with acrosomal maturation was an increase in acrosomal thiols and the formation of disulphides which presumably account for the unusual stability of the wallaby sperm acrosome. The development of motility and progressive motility of tammar wallaby spermatozoa is similar to that of other marsupials and eutherian mammals. Spermatozoa are immotile in the testes and the percentage of motile spermatozoa and the strength of their motility increases during epididymal transit. During passage through the caput and corpus epididymis, spermatozoa first became weakly motile in the proximal caput and then increasingly progressively motile through the corpus epididymis. Tammar wallaby spermatozoa collected from the proximal cauda epididymis had motility not different from ejaculated spermatozoa. Ultrastructural studies indicated that acrosomal condensation involved a complex infolding of the immature acrosome. At spermiation the acrosome of tammar wallaby spermatozoa was a relatively large flat or concave disc which projected laterally and anteriorly beyond the limits of the nucleus. During transit of the epididymal caput and proximal corpus the lateral projections folded inwards to form a cup like structure the sides of which eventually met and fused. The cavity produced by this fusion was lost as the acrosome condensed to its mature form as a small button-like structure contained within the depression on the anterior end of the nucleus. During this process the dorsal surface of the immature acrosome and its outer acrosomal membrane and overlying plasma membrane were engulfed into the acrosomal matrix. This means that the dorsal surface of the acrosomal region of the testicular tammar wallaby sperm head is a transient structure. The dorsal acrosomal surface of the mature spermatozoon appears ultrastructurally to be the relocated ventral surface of the acrosomal projections which previously extended out beyond the acrosomal depression on the dorsal surface of the nucleus of the immature spermatozoon.

Acrosome↗
PubMed1997

Spermiogenesis and spermiation in a marsupial, the tammar wallaby (Macropus eugenii).

Fourteen steps of spermatid development in the tammar wallaby (Macropus eugenii), from the newly formed spermatid to the release of the spermatozoon into the lumen of the seminiferous tubules, were recognised at the ultrastructural level using transmission and scanning electron microscopy. This study confirmed that although the main events are generally similar, the process of the differentiation of the spermatid in marsupials is notably different and relatively more complex than that in most studied eutherian mammals and birds. For example, the sperm head rotated twice in the late stage of spermiogenesis: the shape of the spermatid changed from a T-shape at step 10 into a streamlined shape in step 14, and then back to T-shape in the testicular spermatozoa. Some unique figures occurring during the spermiogenesis in other marsupial species, such as the presence of Sertoli cell spurs, the nuclear ring and the subacrosomal space, were also found in the tammar wallaby. However, an important new finding of this study was the development of the postacrosome complex (PAC), a special structure that was first evident as a line of electron dense material on the nuclear membrane of the step 7 spermatid. Subsequently it became a discontinuous line of electron particles, and migrated from the ventral side of the nucleus to the area just behind the posterior end of the acrosome, which was closely located to the sperm-egg fusion site proposed for Monodelphis domestica (Taggart et al. 1993). The PAC and its possible role in both American and Australian marsupials requires detailed examination. Distinct immature features were discovered in the wallaby testicular spermatozoa. A scoop shape of the acrosome was found on the testicular spermatozoa of the tammar wallaby, which was completely different to the compact button shape of acrosome in ejaculated spermatozoa. The fibre network found beneath the cytoplasm membrane of the midpiece of the ejaculated sperm also did not occur in the testicular spermatozoa, although the structure of the principle piece was fully formed and had no obvious morphological difference from that of the epididymal and ejaculated spermatozoa. The time frame of the formation of morphologically mature spermatozoa in the epididymis of the tammar wallaby needs to be determined by further studies.

Acrosome↗
PubMed1997

Two-photon excitation of 4'-hydroxymethyl-4,5',8-trimethylpsoralen.

Psoralens are a class of pharmaceutical agents commonly used to treat several cutaneous disorders. When irradiated with a mode-locked titanium: sapphire (Ti:sapphire) laser tuned to 730 nm, an aqueous solution of 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) emits blue light. The emission spectrum is centered at 452 nm and is identical to that obtained by one-photon excitation with UVA excitation, and its magnitude depends quadratically on the intensity of laser excitation. These results suggest that two-photon excitation occurs to a potentially photochemically active state. To estimate the two-photon absorption cross section, it was first necessary to measure the emission quantum yield of HMT using 365 nm excitation at room temperature that resulted in a value of 0.045 +/- 0.007. The two-photon absorption cross section of HMT at 730 nm is therefore estimated to be 20 x 10(-50) cm4 s (20 Göppert-Mayer). The excited-state photophysics and photochemistry of psoralens suggest potential applications to cutaneous phototherapy in diseases such as psoriasis and dystrophic epidermolysis bullosa.

Aluminum Oxide↗
PubMed1997

Identification of a 35-kilodalton serovar-cross-reactive flagellar protein, FlaB, from Leptospira interrogans by N-terminal sequencing, gene cloning, and sequence analysis.

During the screening of antibodies to pathogenic leptospires, a murine monoclonal antibody (designated M138) was found to react with various serovars. An antigen of approximately 35 kDa from Leptospira interrogans serovar pomona, which reacted strongly with M138, was characterized by N-terminal amino acid sequencing and identified as a flagellin, a class B polypeptide subunit (FlaB) of the periplasmic flagella. The gene encoding the FlaB protein, flaB, was amplified from the genomic DNA of several pathogenic serovars by PCR with a single pair of oligonucleotide primers, suggesting that FlaB is highly conserved among these serovars. Cloning and sequence analysis of flaB from serovar pomona revealed that it contains an 849-bp open reading frame with a G + C content of 46.88% which encodes a 283-amino-acid protein with a calculated molecular mass of 31.297 kDa and a predicted pI of 9.065. A sequence comparison of flagellin proteins revealed that the amino acid sequence is most variable in the central portion of the serovar pomona FlaB, which is believed to contain specific sequence information and which may thus be useful in the design of DNA or synthetic peptide probes suitable for the detection of infection with pathogenic leptospires.

Amino Acid Sequence↗
PubMed1997

Diminished retinoic acid signaling in hepatic stellate cells in cholestatic liver fibrosis.

Hepatic stellate cells (HSC) participate in liver fibrogenesis via myofibroblastic activation, the extent of which appears to correlate with the loss of cellular vitamin A. The present study has tested a hypothesis that HSC activation is associated with diminished retinoic acid (RA) signaling. Pure HSC were isolated from rats with cholestatic liver fibrosis induced by bile duct ligation (BDL) and sham-operated animals (Sham). Northern blot analysis of HSC RNA from BDL confirmed fibrogenic activation of the cells with enhanced mRNA levels for procollagen-alpha1(I) and transforming growth factor-beta1 (TGF-beta1). Competitive polymerase chain reaction analysis showed selective reductions in the mRNA levels of RA receptor (RAR)-beta and retinoid X receptor (RXR)-alpha to 20 and 17% of the Sham HSC. The mRNA level for cellular retinol binding protein I, a gene with RA responsive element (RARE), was also suppressed by 78% in BDL. The concentrations of all-trans-RA and 9-cis-RA were decreased in HSC from BDL. Nuclear extracts of these cells showed diminished binding activity to the RARE, whereas activity of AP-1, a transcription factor known to be antagonized by RAR and RXR, was enhanced. These results demonstrate diminished RA signaling in HSC from cholestatic liver fibrosis, which appeared to have resulted from RA deficiency and suppressed expression of RAR-beta and RXR-alpha. Furthermore, the reciprocal enhancement of AP-1 activity and coordinately increased expression of an AP-1 responsive gene, TGF-beta1, suggest a permissive role of the diminished RA signaling in promoting AP-1 activity and TGF-beta1 expression.

Animals↗
PubMed1997

Role of iron in NF-kappa B activation and cytokine gene expression by rat hepatic macrophages.

A redox-sensitive nuclear factor, NF-kappa B, induces transcription of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) in macrophages. The present study has investigated the role of iron in NF-kappa B activation and TNF-alpha and IL-6 expression by rat hepatic macrophages (HM). As an in vivo model, cholestatic liver injury was induced in rats by ligation of the common bile duct (BDL). During the first 2 wk after BDL, there was an increase in the hepatic level of thiobarbituric acid-reactive substances (TBARS) that was accompanied by the appearance of protein-malondialdehyde adducts in the periportal region. This increase was reduced after 3 wk. TNF-alpha and IL-6 mRNA levels in HM from the BDL rats were increased at 1 and 2 wk and attenuated at 3 wk. Gel mobility shift assay of HM nuclear extracts demonstrated the similar temporal pattern of enhanced NF-kappa B binding activity. Treatment of the BDL animals with 1,2-dimethyl-3-hydroxypyrid-4-one (L-1), a lipophilic iron chelator, suppressed the increases in hepatic TBARS by 64%, plasma alanine aminotransferase by 45%, and HM TNF-alpha and IL-6 mRNA by > 84%. Concomitantly, the HM NF-kappa B binding activity was reduced close to the level observed in sham-operated rats. Treatment of cultured HM with L-1 also blocked lipopolysaccharide-stimulated NF-kappa B activation and TNF-alpha and IL-6 expression at mRNA and protein levels. These results demonstrate that the iron chelator effectively blocks NF-kappa B activation and coordinate TNF-alpha and IL-6 gene upregulation by HM in cholestatic liver injury or under in vitro lipopolysaccharide stimulation. These findings support a pivotal role for iron in activation of NF-kappa B and cytokine gene expression by HM in vitro and in vivo.

Animals↗
PubMed1997

Carnosine is a novel peptide modulator of intracellular calcium and contractility in cardiac cells.

Myocardial contractile failure is a common cause of morbidity and mortality in patients with ischemic heart disease and systemic inflammatory states such as sepsis. Accumulating evidence indicates that contractile failure is associated with dysregulation of myoplasmic calcium levels. In a search for biochemical causes for contractile dysfunction, we found that the dipeptide carnosine improves cardiac contractility and tested the possibility that carnosine plays a role in the regulation of intracellular calcium. Carnosine increased contractility in a dose-dependent manner (1-10 mM) in isolated perfused rat hearts. and it also increased free intracellular calcium levels in isolated myocytes. Carnosine increased myocyte tension via calcium release from the ryanodine receptor calcium release channel in skinned myocardial fibers and increased open-state probability and dwell time of the isolated ryanodine receptor calcium release channel in lipid bilayers. In addition. we report that carnosine sensitizes the contractile proteins so calcium. These results suggest a novel role for carnosine as a modulator of intracellular calcium and contractility in cardiac tissue.

Animals↗
PubMed1997

[The changes of proportion in hospitalized patients with glaucoma].

OBJECTIVE: To investigate the change of proportion of all kinds of hospitalized patients with glaucoma for the prevention and treatment of the disease. METHODS: 3165 cases in our glaucomatous Department from 1990 to 1996 are classified by their diagnosis, sex and age to analyze the changing feature of proportion. RESULTS: 55.86% of the glaucoma are primary angle closed glaucoma (PACG). Most of the primary angle closed glaucoma (PACG) patients are female over 40 years old. The proportion of POAG is 19.25%, glycocorticoid induced glaucoma (GIG), 4.35%. Young male account for the main parts among these cases with GIG. CONCLUSION: The new trends has emerged in glaucoma practice because the very complicated aspects appear in patients, especially in young adults with POAG and GIG of management.

Adolescent↗
PubMed1997

Comprehensive audit of quality-of-care and quality-of-life for patients with diabetes.

This comprehensive audit was conducted in a three-person general practice with an age-sex-disease register to evaluate care for patients with diabetes using metabolic indicators and validated measures of quality-of-life and patient satisfaction. Medical records were reviewed using criteria derived from guidelines published by Diabetes Australia and New South Wales Health. Self-administered questionnaires mailed to patients included the Diabetes Quality-of-Life measure (DQOL), the Well-Being Questionnaire (WBQ) and the Diabetes Treatment Satisfaction Questionnaire (DTSQ). Record audit for 71 patients with diabetes demonstrated poor control and monitoring. Frequent attenders were no more likely to have had a HgA1c performed than less frequent attenders (P = 0.72). While patient satisfaction with care was high, numerical values for quality-of-life were lower than published overseas norms, indicating a need to support better care in general practice and further research to determine Australian norms.

Adult↗
PubMed1997

Blood groups and transfusion medicine in Taiwan.

There are significant differences in the frequencies of various blood group antigens between Taiwanese and Caucasians, and also in the frequencies of the corresponding alloantibodies. The most interesting discoveries concerning Taiwanese are: 1) The most common ABO subgroups are the B3 phenotype, followed by the Ael phenotype. 2) The secretory H-deficient para-Bombay phenotype (OHm), which results from mutations in five different h genes, is not uncommon. 3) The Le(a+b+) phenotype has a frequency of about 25% and the Le(a+b-) phenotype is absent except in a few of the indigenous groups. 4) Anti-'Mi(a)' is the most common clinically significant alloantibody causing intravascular hemolytic transfusion reactions and hemolytic disease of the newborn. 5) The incidence of the corresponding MiIII blood group phenotype varies among the different ethnic groups, ranging from 0% among descendants of mainland Chinese from north of the Yangste to 88.4% among the Ami tribe. 6) There is an almost complete absence of Di(a) and St(a) antigens among the indigenous populations, in contrast to incidences of greater than 2% among the Chinese ethnic groups. 7) Nearly all (99.67%) Taiwanese are positive for the Rh(D) antigen. Among those with Rh(D) negative phenotype, about 30% have a very weak Rh(D) positive phenotype (Del phenotype). Since the corresponding anti-D antibody is also rarely encountered, routine D typing is not necessary. 8) Some rare blood group phenotypes found in Taiwanese are the i phenotype associated with congenital cataract, DVI phenotype, Dc- phenotype, Jk(a-b-) phenotype, and Lu(a-b-) phenotype.

Blood Group Antigens↗
PubMed1996

Over-expression of p55Cdc inhibits granulocyte differentiation and accelerates apoptosis in myeloid cells.

p55Cdc is a protein identified in cycling mammalian cells. It is highly expressed in proliferating but not in differentiated or growth-arrested cells. Structurally, p55Cdc is similar to the Cdc4 and Cdc20 proteins, which have been proposed to regulate DNA synthesis and mitosis in Saccharomyces cerevisiae. To define the role of p55Cdc during myelopoiesis, we studied the expression and regulation of this protein in response to the hematopoietic growth factors, granulocyte-macrophage colony stimulating factor (GM-CSF) and granulocyte-colony stimulating factor (G-CSF). We analysed the time course of expression of p55Cdc in response to GM-CSF and G-CSF stimulation in the murine factor-dependent myeloid leukemic cell line, 32Dc13, and demonstrated differential regulation of p55Cdc in response to these two growth factors. Over-expression of p55Cdc resulted in acceleration of apoptosis in growth factor- and serum-free conditions, although no difference was observed in the rate of cell proliferation. Decreases in p55Cdc protein levels correlated with cells undergoing apoptosis. p55Cdc over-expression also inhibited granulocyte differentiation of 32Dc13 cells treated with G-CSF. Our studies suggest that p55Cdc regulation is critical for normal cell cycle control during myeloid cell proliferation and differentiation.

Animals↗
PubMed1996

Influence of general anesthetics on a specific neural pathway in Drosophila melanogaster.

The neural pathway that governs an escape response of Drosophila to sudden changes in light intensity can be artificially induced by electrical stimulation of the brain and monitored by electrical recording from the effector muscles. We have refined previous work in this system to permit reliable ascertainment of two kinds of response: (i) a short-latency response that follows from direct excitation of a giant fiber neuron in the interior of the fly brain and (ii) a long-latency response in which electrical stimulation triggers neurons in the optic ganglia that ultimately impinge on the giant fiber neuron. The general anesthetic halothane is reported here to have very different potencies in inhibiting these two responses. The long-latency response is obliterated at concentrations similar to those that cause gross behavioral effects in adult flies, whereas the short-latency response is only partially inhibited at doses that are 10-fold higher. Three other volatile anesthetic agents show a similar pattern. Thus, as in higher organisms, the Drosophila nervous system is differentiated into components of high and low sensitivity to general anesthetics. Moreover, this work shows that one of the sensitive components of the nervous system lies in the optic lobe and is readily assayed by its effect on downstream systems; it should provide a focus for exploring the effects of genetic alteration of anesthetic sensitivity.

Anesthetics, General↗
PubMed1996

Heterogeneity of the human Secretor alpha(1,2)fucosyltransferase gene among Lewis(a+b-) non-secretors.

The human Secretor alpha (1,2)fucosyltransferase gene determines the ABH secretor status and influences the Lewis phenotype of an individual. Two different se alleles with point mutations, C571 to T and G849 to A respectively, in the coding region were identified in Le(a+b-) non-secretors from one of the Taiwanese indigenous groups. The base substitutions predict the alteration of Arg191 and Trp283 to stop codons respectively, resulting in deletion of the Secretor enzyme's C-terminal segment. Both alleles of the Secretor locus in all Le(a+b-) non-secretors, but not in Le(a+b-) secretors, were further demonstrated to be either one of these two se alleles with nonsense mutations. These results suggest two new molecular bases for the null se allele responsible for the formation of the non-secretor phenotype.

ABO Blood-Group System↗
PubMed1996

A new method for estimating high mutation rates in cultured cells.

Fluctuation analysis allows for the determination of mutation rates in cell cultures in vitro. As originally described by Luria and Delbruck and extended by Lea and Coulson and by Capizzi and Jameson, this analysis has been useful in estimating mutation rates in cultured cells where the frequency of mutational events is low. However. in cultures where high mutation rates and multiple independent mutation events occur, leading to the accumulation of many mutant cells, these standard methods may not apply. Here, we present a new method for the estimation of mutation rates based on the assumption that multiple events may contribute to the accumulation of mutant cells. We compared mutation rates determined by Lea and Coulson's and by Capizzi and Jameson's methods with those determined by our method using experimental and stimulated data from our studies of immunoglobulin gene mutation and isotype switching in B lymphocyte cultures. The three methods resulted in very different calculated rates when many mutants were present in the culture, such as when mutation rates were high, while only small differences in calculated rates were found when mutants were rare. Unlike previous fluctuation analysis calculations, our method is applicable for the estimation of both low and high rates.

Animals↗
PubMed1996

Formation of chimeric DNA primer extension products by template switching onto an annealed downstream oligonucleotide.

Oligodeoxynucleotide sequences are described that anneal to a template downstream of a priming site. During polymerase-catalyzed extension of the primer, the extending primer shifts from the original template to a segment of the annealed oligonucleotide that acts as an alternative template. The resulting chimeric extended primer has one segment that is complementary to the template and a second segment that is complementary to the oligonucleotide. The influence of the sequence elements of the oligonucleotide and the reaction conditions on template switching have been explored. The sequence requirements for template switching are compared to those for transposon excision.

Base Sequence↗
PubMed1996

Heparin and heparan sulfate block angiotensin II-induced hypertrophy in cultured neonatal rat cardiomyocytes. A possible role of intrinsic heparin-like molecules in regulation of cardiomyocyte hypertrophy.

BACKGROUND: Heparan sulfate, one of the primary components of extracellular matrix, is a potent antigrowth factor in certain types of cells. To elucidate a possible role of endogenous heparin-like molecules in regulating cardiomyocyte hypertrophy, we investigated the effects of heparin and heparan sulfate on angiotensin (Ang) II-induced hypertrophy in cultured neonatal rat cardiomyocytes. METHODS AND RESULTS: Competitive [3H]heparin binding assay showed that cardiomyocytes had specific binding sites for heparin. In situ [3H]heparin binding assay demonstrated that heparin, which rapidly bound to the cardiomyocyte surface, was subsequently accumulated around the nuclei, suggesting that heparin might work in the nucleus. Cotreatment with heparin (20 micrograms/mL) completely inhibited increased cell surface area by Ang II (10(-6) mol/L). Increased [3H]leucine incorporation by Ang II was reduced by heparin dose-dependently. The inhibitory effect of heparin on Ang II-induced cardiomyocyte hypertrophy also was confirmed by Northern blot analysis: heparin dose-dependently inhibited skeletal alpha-actin and atrial natriuretic peptide gene expression, genetic markers for cardiomyocyte hypertrophy. Heparan sulfate showed similar inhibitory effects on cell surface area, [3H]leucine incorporation, and skeletal alpha-actin gene expression. Treatment with heparinase I or III, which specifically digests the disaccharide chains of endogenous heparin-like molecules, upregulated protein synthesis and skeletal alpha-actin and atrial natriuretic peptide gene expression in cardiomyocytes. CONCLUSIONS: Our findings in this study strongly suggest that heparin and heparan sulfate are potent inhibitors of cardiomyocyte hypertrophy and that endogenous heparin-like substances negatively regulate cardiomyocyte hypertrophy.

Angiotensin II↗
PubMed1996

Mild hypoxia induces hypertrophy of cultured neonatal rat cardiomyocytes: a possible endogenous endothelin-1-mediated mechanism.

Hypoxic or ischemic stresses on cardiomyocytes may cause a variety of compensatory responses including cell hypertrophy. In this study, we examined whether hypoxia induces hypertrophy of cardiomyocytes in vitro and whether hypoxia-induced hypertrophy is inhibited by an endothelin A receptor antagonist (BQ123). Neonatal rat cardiomyocytes were cultured in 10% O2/85% N2/5% CO2 or 95% N2/5% CO2 to produce a mild or severe hypoxic condition, respectively. Cardiomyocytes exposed to severe hypoxia revealed degenerative morphological changes and a decrease of cell number, suggesting the toxicity of severe hypoxia on cardiomyocytes. In contrast, cardiomyocytes with mild hypoxia developed hypertrophy; cell surface area of cardiomyocytes as evaluated by an image analyser system increased by 1.6-fold over control after 48 h. [3H]leucine incorporation into the cells was significantly increased by mild hypoxia but decreased by severe hypoxia, mRNA level of skeletal alpha-actin, a genetic marker of cardiac hypertrophy, up-regulated after 6-24 h by mild hypoxia. A transient increase of preproET-1 mRNA and a time-dependent increase of ET-1 protein in the culture medium were also observed in cardiomyocytes exposed to mild hypoxia. BQ123 partially inhibited either hypoxia-induced [3H]leucine incorporation or skeletal alpha-actin mRNA in a dose-dependent manner. These data suggest that mild hypoxia induces hypertrophy of cardiomyocytes and that activation of endogenous ET-1 may, at least in part, mediate this hypertrophic responses as an autocrine/ paracrine factor.

Actins↗