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Biomedical subjects

W M Lee

Publications and source records attributed to W M Lee.

At least 55 records · Page 3Linked to original sources
PubMed2001

Clinical significance of microvessel density in multiple myeloma patients.

To investigate the role of angiogenesis in multiple myeloma (MM), bone marrow biopsy from 75 adults with newly diagnosed, untreated MM were evaluated. Microvessels were scored in at least 3 areas ( x 200 fields) of the highest microvessel density in representative sections of each bone marrow specimen using immunohistochemistry for CD34. Prognostic variables were also evaluated for the overall survival. Microvessel counts were significantly higher in patients with MM (n=69.42+/-9.67), compared with control (n=26.81+/-2.85). Microvessel density had a weak correlation with percentage of bone marrow plasma cells. By univariate analysis, age, beta2-microglobulin, serum albumin, serum creatinine, serum calcium, hemoglobin, platelet count, and bone marrow plasma cell percentage were correlated with survival. By multivariate analysis, age, serum albumin, serum creatinine, hemoglobin, platelet count and bone marrow plasma cell percentage were correlated with overall survival, whereas microvessel density was not. In summary, microvessel density in bone marrow of MM is significantly increased compared to control, but was not correlated with overall survival. Further studies regarding angiogeneic molecules are needed to determine the functional role of angiogenesis in MM.

Adult↗
PubMed2000

Chronic hepatitis B virus infection: treatment strategies for the next millennium.

Chronic hepatitis B virus (HBV) infection is a leading cause of cirrhosis and hepatocellular carcinoma worldwide. Its prevalence approaches 10% in hyperendemic areas, such as southeast Asia, China, and Africa. Although chronic HBV infection is seen less frequently in North America and Europe, an estimated 1.25 million persons in the United States are infected. In the past decade, revolutionary strides have been made toward the treatment of chronic HBV infection. Interferon-alpha was once the only available therapy but has recently been joined by the nucleoside analogues, the most extensively studied of which is lamivudine. Interferon therapy continues to have a role in the treatment of a carefully selected group of patients. Lamivudine therapy, which has less stringent selection criteria, suppresses HBV DNA in almost all treated patients: Seventeen percent to 33% experience loss of hepatitis B e antigen, and 53% to 56% have a histologic response. Extended lamivudine treatment leads to the development of a specific lamivudine-resistant virus with base-pair substitutions at the YMDD locus of the DNA polymerase. Newer nucleoside analogues and other immunomodulator therapies are being investigated. In the future, combination therapy with different classes of agents may yield improved response rates and delay the development of resistance.

Adjuvants, Immunologic↗
PubMed2000

Rat testicular myotubularin, a protein tyrosine phosphatase expressed by Sertoli and germ cells, is a potential marker for studying cell-cell interactions in the rat testis.

The full-length cDNA encoding the entire open reading frame (ORF) of rat myotubularin (rMTM) was isolated from a rat testis expression library by PCR. Among the three approximately 2.9-kb cDNAs that were sequenced, one clone was different from the other two clones. It contained seven extra amino acids of FVVLNLQ; this short stretch of extra sequence was found between Gln(421) and Phe(422) within the SET (Suvar3-9, Enhancer-of-zeste, Trithorax) interacting domain (SID) of rMTM. The rMTM ORF had 1,713 bp encoding for a 571 amino acid polypeptide and a calculated molecular weight of 65.8 kDa. A comparison between its deduced amino acid sequence and the GenBank database using BLAST revealed a 53.1% identity with human myotubularin protein (hMTM1), which is a member of the protein tyrosine phosphatase (PTP) family associated with X-linked myotubular myopathy. A 22 amino acid peptide NH(2)-TKVNERYELCDTYPALLAVPAN was synthesized based on the deduced amino acid sequence of rMTM and used for antibody production. By using immunoblot analysis, a 66-kDa protein was indeed detected in both Sertoli and germ-cell cytosols. rMTM mRNA was found in various tissues but was predominantly expressed in the testis, ovary, and skeletal muscle. Sertoli cell rMTM expression was stimulated by germ cells and enhanced when inter-Sertoli junctions were being assembled in vitro. A drastic reduction in testicular rMTM steady-state mRNA level correlated with the depletion of germ cells from the testis in vivo following either glycerol or lonidamine treatment. These results indicate that rMTM is a rat homologue of hMTM1 that may be a useful marker in monitoring the events of cell-cell interactions in the testis.

Amino Acid Sequence↗
PubMed2000

Troglitazone-induced fulminant hepatic failure. Acute Liver Failure Study Group.

The three reported cases demonstrate that troglitazone is an idiosyncratic hepatotoxin that can lead to irreversible liver injury. Thus, troglitazone should be prescribed with caution and should not be used as a first-line agent in the treatment of type II DM when potentially less toxic alternatives are available. It remains to be seen whether the hepatotoxicity associated with troglitazone is a drug-class effect or specific to troglitazone. Other thiazolidinediones currently in clinical trials may be able to provide the therapeutic benefits of troglitazone without significant hepatotoxicity. If troglitazone is used, frequent monitoring of serum aminotransferases and symptoms is mandatory. However, as illustrated by these and other cases reported to date, the onset of troglitazone-induced liver injury is insidious and temporally variable. Thus, the value of close monitoring and when, if ever, it is safe to stop such monitoring are currently unclear.

Chromans↗
PubMed2000

A phenomenological study of early nursing experiences in Hong Kong.

The experience of primary professional socialization is crucial for neophytes to learn to become a nurse. These early nursing encounters may also have long-term effects on professional development of individual nurses. However, research into the early experiences of nurses has been poorly documented. This study endeavours to reveal the early lived nursing experience amongst a group of nurses in Hong Kong. This study adopts a phenomenological approach which involves the thematic analysis of the critical incidents provided by 77 subjects. Findings revealed that incidents associated with death and dying, and clinical learning embracing interpersonal relations and professional development, were the most memorable events. Nurses were in general not equipped adequately to communicate with the dying and the grieving relatives. The subjects disclosed that positive clinical encounters confirmed their value of nursing work and motivated them to stay in the profession. Conversely, the negative experiences made them seriously consider leaving nursing. A number of implications for nursing education have been drawn from the research findings.

Existentialism↗
PubMed2000

Acute hepatic failure: a Western perspective.

Acute hepatic failure (AHF) is an uncommon, devastating syndrome, which results in death or the need for liver transplantation in more than 50% of cases. While AHF has numerous causes, most cases are due to viral hepatitis and drug toxicity or idiosyncratic reactions. A significant group with indeterminate causation remains, despite careful investigation. In many of these cases a viral aetiology is suspected, although yet not proven. Major differences exist in the aetiology of AHF between the West and Eastern countries. A wider range of aetiologies exists in the West. Common causes include acetaminophen toxicity and idiosyncratic drug reactions, while viral hepatitis is less frequent. Hepatitis E infection is rarely seen in Western countries in contrast to its high prevalence in the East. The mainstay of AHF management is supportive care in an intensive care unit. Liver transplantation is now the standard of care in many Western liver units for individuals who have a less than 20% probability of survival. Lack of availability of donor livers at short notice remains a significant problem. Methods of liver support used while waiting for a donor liver or for the native liver to regenerate include bioartificial livers, extracorporeal liver-assist devices, extracorporeal whole organ perfusion (human and transgenic pig) and hepatocyte transplantation. The effectiveness of these methods remains unproven and awaits controlled clinical trials. Both transplantation and liver-support methods require specialized units and expensive and complicated equipment. Further research is necessary to identify modalities of therapy that would be effective as well as widely accessible.

Acetaminophen↗
PubMed2000

Actin-containing sera from patients with adult respiratory distress syndrome are toxic to sheep pulmonary endothelial cells.

Actin released from damaged cells after a variety of tissue injuries appears to be involved in multiple organ dysfunction syndrome. Under experimental conditions, when the quantity of actin present in plasma is made to exceed the protective capacity of the actin-scavenging mechanism, microembolism and pulmonary vascular angiopathy have been noted in rats. It remains to be determined whether this injury is a result of a direct toxic effect or occurs indirectly via platelet activation or fibrin interactions. We examined the effect of sera from patients with adult respiratory distress syndrome (ARDS), as well as G-actin added to normal serum, on the viability, morphology, and function of cultured sheep pulmonary artery endothelial cells (SPAEC). Both patient sera and normal sera to which actin was added were toxic in the cell culture model; this toxicity could be abrogated, at least partially, by preincubation with gelsolin, which is known to complex with actin. A significant portion of the toxicity of sera from patients with ARDS was sensitive to heat (56 degrees C), suggesting an important role of complement. Sera from patients with ARDS were shown to contain filaments of F-actin by immunoblot and rhodamine phalloidin staining after ultracentrifugation. Thus, saturation of the actin-scavenging system by addition of exogenous G-actin to plasma produces direct pulmonary endothelial cell injury. Furthermore, plasma from patients with ARDS secondary to bacterial pneumonia is toxic to SPAEC, and a small but significant contributory role of actin is apparent in these studies.

Actins↗
PubMed2000

Sertoli cell prostaglandin D2 synthetase is a multifunctional molecule: its expression and regulation.

PGD2 synthetase (PGD-S; PGH2 D-isomerase; EC 5.3.99.2) is a bifunctional protein first identified in the mammalian brain. It acts as a PGD2-producing enzyme and a retinoid transporter. PGD-S is present in the testis, where its protein and messenger RNA levels are similar to those in the brain. In view of its diversified regulatory functions, we investigated its regulation using primary cultures of Sertoli cells in vitro to assess its role in the testis. When Sertoli cells were cultured in serum-free medium to allow the formation of specialized junctions, it was found that PGD-S expression increased steadily with time, coinciding with the formation of inter-Sertoli junctions in vitro. However, neither germ cells (using a Sertoli/germ cell ratio between 1:1 and 1:30 when Sertoli cells were cultured at a density of 5x10(4) cells/cm2) nor germ cell-conditioned medium affected the expression of Sertoli cell PGD-S in vitro. These results thus unequivocally demonstrated that germ cells do not play a role in regulating testicular PGD-S expression. Although FSH, dihydrotestosterone, and testosterone had no apparent effect on Sertoli cell PGD-S expression, the addition of progesterone(1x10(-11) to 1x10(-9) M) and T3 (1x10(-11) to 1x10(-9) M) to Sertoli cell cultures elicited a significant increase in PGD-S expression by as much as 4.5- and 2.5 fold, respectively. As PGD-S is a known retinoid transporter, the effects of all-trans-retinoic acid and all-trans-retinal on Sertoli cell PGD-S expression were also assessed. Both compounds were found to induce Sertoli cell PGD-S expression. In summary, PGD-S is a putative Sertoli cell product whose expression is regulated by progesterone, metabolites of vitamin A, and T3. In view of its dual biological properties, a study of its regulation and physiology will yield new insights into understanding its role in the testis.

Aging↗
PubMed2000

The rabbit sex hormone-binding globulin gene: structural organization and characterization of its 5-flanking region.

Sex hormone-binding globulin (SHBG) transports sex steroids in the blood. In humans and rabbits, the gene encoding SHBG (shbg) is expressed primarily in the liver and testis, whereas the testis is the major site of shbg expression in rodents postnatally. Sequence analysis has revealed that rabbit shbg (rbshbg) spans 2.5 kb and comprises eight exons with consensus splice sites at all exon-intron junctions. The major transcription start site ofrbshbg is located 52 bp upstream from the translation initiation codon for the rabbit SHBG precursor. Unlike the situation in humans and rats, rbshbg transcripts contain no alternative exon 1 sequences in the liver or testis, and this suggests that the rbshbg 5'-flanking region plays an equally important role in controlling transcription of this gene in these tissues. Like the human and rat shbg promoter sequences, the rbshbg proximal promoter lacks a typical TATA box. It also contains several transcription factor-binding sites, but deoxyribonuclease I footprinting experiments indicated that the human and rabbit shbg proximal promoters interact quite differently with proteins extracted from rabbit liver nuclei. However, the predominant footprint on the rbshbg promoter is conserved at the same position within the human shbg (hshbg) promoter and includes consensus binding sites for the transcription factor nuclear factor- 1. Transient transfection studies of the rbshbg 5'-flanking sequence (893 bp) revealed regions that actively enhance and repress its activity in human hepatoblastoma and mouse Sertoli cells, but not in Chinese hamster ovary cells. Like the rat shbg proximal promoter, the rbshbg 5'-flanking sequence lacks a region that corresponds to a cis-element, designated footprinted region 4 in the hshbg proximal promoter. Furthermore, the hshbg promoter footprinted region 3 sequence is poorly conserved in rbshbg, and when mutated to resemble the corresponding human sequence it increased the transcriptional activity of the rbshbg promoter by 7-fold in hepatoblastoma cells. Thus, the rabbit and hshbg promoters appear to be controlled by a different set of transcriptional regulators. Further comparisons of their functional activities may shed light on species-specific differences in the spatial and temporal expression of this gene, the products of which play important roles in regulating sex steroid access to target cells.

Animals↗
PubMed1999

Angiopoietin-1 and -2 coiled coil domains mediate distinct homo-oligomerization patterns, but fibrinogen-like domains mediate ligand activity.

Activity of endothelial Tie2 receptor tyrosine kinase is modulated by two naturally occurring, secreted ligands, angiopoietin-1 and -2, which have opposing effects on its phosphorylation. Receptor tyrosine kinase activation requires receptor dimerization/multimerization, which, for many receptors, is mediated by homo-oligomeric ligands binding to and bridging receptor molecules. We show here that angiopoietin-1 and -2 form distinct arrays of disulfide-linked homo-oligomeric complexes. Their mobilities on nonreducing gels suggest that angiopoietin-2 exists predominantly as a homodimer but also forms higher order multimers. In contrast, angiopoietin-1 forms some homotrimers, but predominantly exists in higher order multimers. These two structurally related, 60% homologous ligands are predominantly composed of an amino-terminal coiled coil domain and a carboxyl-terminal fibrinogen-like domain. We show that their distinct oligomerization patterns are determined by their coiled coil domains and, furthermore, that their coiled coil domains, but not their fibrinogen-like domains, are sufficient to mediate formation of disulfide-linked homo-oligomers. In contrast, the differential effects of these ligands on endothelial Tie2 phosphorylation is mediated by their fibrinogen-like domains. We conclude from these studies that the coiled coil and fibrinogen-like domains of the angiopoietins have distinct functions with the coiled coil domain mediating ligand homo-oligomerization and the fibrinogen-like domain mediating ligand activity.

Angiopoietin-1↗
PubMed1999

Hypoxia-mediated apoptosis from angiogenesis inhibition underlies tumor control by recombinant interleukin 12.

The role of angiogenesis inhibition in the antitumor activity of recombinant murine interleukin 12 (rmIL-12) was studied in K1735 murine melanomas, the growth of which is rapidly and markedly suppressed by rmIL-12 treatment. On the basis of the prediction that tumor ischemia should result from therapeutic angiogenesis inhibition, tumor cell hypoxia was evaluated as a marker of ischemia using the EF5 [2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)aceta mide] approach. This method measures intracellular binding of the nitroimidazole EF5, which covalently binds to cellular macromolecules selectively under hypoxic conditions. Whereas 1 week of rmIL-12 treatment effectively inhibited K1735 cell-induced angiogenesis in Matrigel neovascularization assays, 2 weeks of treatment were needed before severe tumor cell hypoxia was detected in K1735 tumors. The hypoxia that developed was regional and localized to tumor areas distant from blood vessels. The great majority of severely hypoxic tumor cells were apoptotic, and in vitro studies indicated that the degree of hypoxia present within treated tumors was sufficient to trigger K1735 apoptosis. Tumor cell apoptosis was also prevalent in the first week of rmIL-12 treatment when few cells were hypoxic. In vitro studies indicated that this non-hypoxia-related apoptosis was induced directly by IFN-gamma produced in response to rmIL-12 administration. These studies reveal that rmIL-12 controls K1735 tumors initially by IFN-gamma-induced apoptosis and later by hypoxia-induced apoptosis. They also establish hypoxia as an expected result of tumor angiogenesis inhibition and a mediator of its therapeutic effect.

Animals↗
PubMed1999

Regulation of anion secretion by cyclo-oxygenase and prostanoids in cultured epididymal epithelia from the rat.

1. The role of cyclo-oxygenase (COX) in the regulation of anion secretion (measured as short- circuit current, Isc) in cultured epididymal epithelia from immature rats was investigated. 2. COX inhibitors attenuated the increase of anion secretion caused by bradykinin (LBK) but had no effect on that caused by PGE2, suggesting that prostaglandin synthesis mediates the secretory response of the tissues to LBK. 3. The apparent IC50 values for indomethacin, piroxicam and L-745,337 in inhibiting the LBK-induced Isc were 0.14, 1.34 and 15.7 microM, respectively. This order of potency: indomethacin > piroxicam > L-745,337 >> DFU suggests the involvement of the COX-1 isozyme in the mediation of the secretory response to LBK. 4. Among the COX products (prostaglandins, thromboxane and prostacyclins) tested, only PGE2 and, to a much lesser extent, PGF2alpha stimulated anion secretion by cultured rat epididymal epithelia. 5. The effect of PGE2 was mimicked by 11-deoxyl PGE1, a specific prostaglandin E (EP)2/4 receptor agonist, but not by sulprostone, a specific EP1/3 receptor agonist, indicating that cyclic AMP-coupled EP2/4 receptors are involved in the LBK-stimulated anion secretion. 6. A reverse transcriptase-polymerase chain reaction study detected the expression of COX-1 and COX-2 mRNA in intact rat epididymis and in cultured epididymal epithelia. The expression of COX-1 mRNA was reduced by LBK by 44 %. 7. Immunohistochemical studies demonstrated the presence of COX-1 immunoreactivity in the basal cells of the intact rat epididymis. By comparison, COX-2 immunoreactivity was detected in the apical pole of the principal cells. 8. The role of COX in the formation of the epididymal microenvironment and the implication of long term administration of non-steroidal anti-inflammatory drugs (NSAIDs) on male fertility are discussed.

Animals↗
PubMed1999

Study on the formation of specialized inter-Sertoli cell junctions in vitro.

An in vitro culture system using Sertoli cells was employed to assess the expression of component genes pertinent to occluding junctions (OJ) (such as zonula occludens-1, ZO-1), anchoring junctions (AJ) (such as N-cadherin and beta-catenin), and communicating gap junctions (GJ) (such as connexin 33, Cx33) when they are being formed in vitro. Freshly isolated Sertoli cells from 20-day-old rats with a purity of greater than 90% were cultured either at low- (2.5 x 10(4) cells/cm(2)) or high-cell density (0.6 x 10(6) cells/cm(2)) on Matrigel-coated dishes for 7 days in vitro to allow the establishment of specialized junctions. In low cell density Sertoli cell cultures, specialized OJ such as tight junctions did not form during the entire culture period when assessed by the transepithelial electrical resistance (TER). In high cell density cultures, there was an increase in ZO-1 expression in days 1 to 3 preceding the establishment of tight junctions by day 4. When Sertoli cells were cultured at both cell densities, there was a transient increase in Sertoli cell N-cadherin expression, which peaked by days 4-5, suggesting the time course for the establishment of AJ may overlap with the OJ. A significant increase in the expression of Sertoli cell beta-catenin was also detected by days 5-7 in the high but not low cell density cultures. The expression of Cx33 was also enhanced at days 4-5 in both high and low density cultures. These results suggest that OJ, AJ, and GJ are formed between Sertoli cells in high density cultures, whereas OJ cannot be formed in low density cultures. A full-length cDNA clone coding for rat testicular beta-catenin was also isolated. The deduced amino acid sequence of rat beta-catenin yielded a 781 amino acid polypeptide which displayed a 99.9% identity with the mouse homolog. Conditioned medium of germ cells induced a dose-dependent stimulation on Sertoli cell beta-catenin expression, suggesting germ cells may affect the N-cadherin/beta-catenin-mediated signal transduction pathway. In summary, this study illustrates several target genes can be used as molecular markers to monitor the inter-Sertoli junction formation. This system should be applicable to screen new male contraceptives in vitro targeted at the interference of junction formation by disrupting the timely expression of genes necessary for junction establishment and/or maintenance.

Amino Acid Sequence↗