Search PubMed⌕ Search

Biomedical subjects

H Chen

Publications and source records attributed to H Chen.

At least 631 records · Page 35Linked to original sources

Epidermal growth factor pathway substrate 15, Eps15.

Eps15 was originally identified as a substrate for the kinase activity of the epidermal growth factor receptor (EGFR). Eps15 has a tripartite structure comprising a NH2-terminal portion, which contains three EH domains, a central putative coiled-coil region, and a COOH-terminal domain containing multiple copies of the amino acid triplet Aspartate-Proline-Phenylalanine. A pool of Eps15 is localized at clathrin coated pits where it interacts with the clathrin assembly complex AP-2 and a novel AP-2 binding protein, Epsin. Perturbation of Eps15 and Epsin function inhibits receptor-mediated endocytosis of EGF and transferrin, demonstrating that both proteins are components of the endocytic machinery. Since the family of EH-containing proteins is implicated in various aspects of intracellular sorting, biomolecular strategies aimed at interfering with these processes can now be envisioned. These strategies have potentially far reaching implications extending to the control of cell proliferation. In this regard, it is of note that Eps15 has the potential of transforming NIH-3T3 cells and that the eps15 gene is rearranged with the HRX/ALL/MLL gene in acute myelogeneous leukemias, thus implicating this protein in the subversion of cell proliferation in neoplasia.

Adaptor Proteins, Signal Transducing↗

Direct biophysical characterization of human apolipoprotein A-1 in ISCOMs.

Human apolipoprotein A-1 was formulated in "Immune Stimulating Complexes" (ISCOMs). The structure of the protein in ISCOMs was examined directly using several biophysical techniques including Fourier transform infrared (FTIR) spectroscopy, near UV circular dichroism (CD), and fluorescence spectroscopy. Amide I FTIR data indicate that human apolipoprotein A-1 displays a slightly increased alpha-helical content after its incorporation into ISCOMs. Near UV CD and tryptophan fluorescence data suggest that association with ISCOMs results in the tryptophan residues of the protein experiencing a relatively hydrophobic environment, motional restriction, and local electrostatic interactions. These observations are consistent with an increased order in the protein structure upon incorporation in ISCOMs. In addition, biomolecular interaction analysis (BIA), based on surface plasmon resonance (SPR) measurements, suggests that the binding affinity of human apolipoprotein A-1 to a monoclonal anti-human apolipoprotein A-1 antibody is moderately decreased (by 20%) after its incorporation into ISCOMs. This study demonstrates that these biophysical techniques can be used to noninvasively monitor integrity of or changes in secondary and tertiary structure of proteins within the ISCOM particles without the need for protein extraction.

Apolipoprotein A-I↗

Effects of phosphatidylinositol 4,5-bisphosphate and neomycin on phospholipase D: kinetic studies.

The kinetics of phosphatidylcholine-specific phospholipase D activated by phosphatidylinositol 4,5-bisphosphate (PIP2) and inhibition by neomycin were studied in an enzyme preparation partially purified from human hepatocarcinoma cell line. It was found that phospholipase D was marginally activated by phosphatidyl-4-phosphate (PIP) and phosphatidylethanolamine (PE). In contrast, it was considerably activated by PIP2 in different concentration of phosphatidylcholine (PC). Sphingomyelin (SM), lysophosphatidylcholine (LPC) and phosphatidylserine (PS) were neither substrates nor inhibitors of the phospholipase D. PIP, induced an allosteric effect on phospholipase D and a negative cooperative effect with respect to phosphatidylcholine as indicated in the Lineweaver-Burk plot. In the absence of PIP2, a straight line was obtained, whereas a downward concave curve was observed in the presence of 25 microM of PIP2. The Hill coefficient and the apparent K(m) of phosphatidylcholine in the presence of 25 microM PIP, were calculated to be 0.631 and 10.79 mM, respectively. PIP2 also increased the maximal velocity (Vmax) of the phospholipase D reaction, suggesting that the affinity of substrate to enzyme was decreased, and the turnover number of the enzyme (kcat) was increased by PIP2. The activation of phospholipase D by PIP2 was dose dependent up to 50 microM of PIP2. The Ka of PIP2 was 15.8 mM. Neomycin, a polycationic glycoside, was shown to be an uncompetitive inhibitor of phospholipase D, and revealed the formation of a neomycin-PIP2 complex. The Ki of neomycin was estimated to be 8.7 mM.

Carcinoma, Hepatocellular↗

Generation of mice expressing the human glucagon receptor with a direct replacement vector.

The process of evaluating the in vivo efficacy of non-peptidyl receptor antagonists in animal models is frequently complicated by failure of compounds displaying high affinity against the human receptors to show measurable affinity at the corresponding rodent receptors. In order to generate a suitable animal model in which to evaluate the in vivo activity of non-peptidyl glucagon receptor antagonists, we have utilized a direct targeting approach to replace the murine glucagon receptor with the human glucagon receptor gene by homologous recombination. Specific expression of the human glucagon receptor (GR) in the livers of transgenic mice was confirmed with an RNase protection assay, and the pharmacology of the human GRs expressed in the livers of these mice parallels that of human GR in a recombinant CHO cell line with respect to both binding of 125I-glucagon and the ability of glucagon to stimulate cAMP production. L-168,049, a non-peptidyl GR antagonist selective for the human GR shows a 3.5 fold higher affinity for liver membrane preparations of human GR expressing mice (IC50 = 172 +/- 98 nM) in the presence of MgCl2 in marked contrast to the measured affinity of the murine receptor (IC50 = 611 +/- 197 nM) for this non-peptidyl antagonist. The human receptors expressed are functional as measured by the ability of glucagon to stimulate cAMP production and the selectivity of this antagonist for the human receptor is further verified by its ability to block glucagon-stimulated cyclase activity with 5 fold higher potency (IC50 = 97.2 +/- 13.9 nM) than for the murine receptor (IC50 = 504 +/- 247 nM). Thus we have developed a novel animal model for evaluating GR antagonists in vivo. These mice offer the advantage that the regulatory sequences which direct tissue specific and temporal expression of the GR have been unaltered and thus expression of the human gene in these mice remains in the normal chromosomal context.

Animals↗

Pharmacokinetics and biologic activity of the novel mast cell inhibitor, 4-(3-hydroxyphenyl)-amino-6,7-dimethoxyquinazoline in mice.

PURPOSE: The purpose of the present study was to examine the pharmacodynamic and pharmacokinetic features of the novel mast cell inhibitor 4-(3'-Hydroxyphenyl)-amino-6,7-dimethoxyquinazoline (WHI-P180) in mice. METHODS: A high performance liquid chromatography (HPLC)-based quantitative detection method was used to measure plasma WHI-P180 levels in mice. The plasma concentration-time data was fit to a single compartment pharmacokinetic model by using the WinNonlin program to calculate the pharmacokinetic parameters. A cutaneous anaphylaxis model was used to examine the pharmacodynamic effects of WHI-P180 on anaphylaxis-associated vascular hyperpermeability. RESULTS: The elimination half-life of WHI-P180 in CD-1 mice (BALB/ c mice) following i.v., i.p., or p.o. administration was less than 10 min. Systemic clearance of WHI-P180 was 6742 mL/h/kg in CD-I mice and 8188 mL/h/kg in BALB/c mice. Notably, WHI-P180, when administered in two consecutive nontoxic i.p. bolus doses of 25 mg/kg, inhibited IgE/antigen-induced vascular hyperpermeability in a well-characterized murine model of passive cutaneous anaphylaxis. CONCLUSIONS: WHI-P180 is an active inhibitor of IgE-mediated mast cell responses in vitro and in vivo. Further preclinical characterization of WHI-P180 may improve the efficacy of WHI-P180 in vivo and provide the basis for design of effective treatment and prevention programs for mast cell mediated allergic reactions.

Animals↗

Identification of an adhesion molecule expressed on adult T cell leukemia cells derived from a patient with gastrointestinal involvement: implication for a possible role of integrin beta 7 in leukemic cell infiltration into intestinal mucosa.

Patients with adult T cell leukemia (ATL) often manifest leukemic cell infiltration into various organs such as lung, liver, skin, and gut. To analyze the mechanism of intestinal infiltration of ATL cells, we made mAbs against ATL-43T, a human T cell line derived from an ATL patient with severe intestinal mucosal infiltration. One of the mAbs, named H920, was noted for a high and relatively specific reactivity with ATL-43T. Molecular cloning was done to identify this molecule and disclosed that the Ag molecule was identical to integrin beta 7. Since integrin beta 7 and its ligand MAdCAM-1 had been reported to mediate homing of lymphocytes to endothelial cells in intestinal mucosa, we next examined wither ATL-43T cells could adhere to MAdCAM-1+ cells. Human MAdCAM-1 transfectants of MMCE, a mouse epithelial cell line, were made and used to evaluate cell adhesion mediated by integrin beta 7 and MAdCAM-1. Considerable levels of cell adhesion were observed between ATL-43T and the transfectant cells, which was inhibited by H920 mAb in a dose-dependent manner. Furthermore, peripheral blood leukemic cells or lymphoma cells from 10 ATL patients were examined for expression of integrin beta 7 with regard to organ involvement. Samples from three patients with gastrointestinal tract involvement showed considerably higher expression of integrin beta 7. These results suggest that integrin beta 7 may play a role in adhesion and subsequent infiltration of a certain type of ATL cells into intestinal mucosa.

Adult↗

HLA-DR-DQ alleles and HLA-DP alleles are independently associated with susceptibility to different stages of post-schistosomal hepatic fibrosis in the Chinese population.

Abstract: Evaluation of human leukocyte antigen (HLA) class I and class II genes was performed on patients from China with Schistosomiasis japonica. Patients were categorized as grade 0 (n=44), grade I (n=81), grade II (n=99), or grade III (n=6) based on increasing severity of hepatic fibrosis due to repeated Schistosoma japonicum infections. These results show that the HLA-DRB1*1101-DQA1*0501-DQB1*0301 (Pc<0.02) and HLA-DRB1*1501-DRB5*0101 (Pc<0.02) haplotypes are associated with protection and susceptibility to grade I fibrosis, respectively, and that the HLA-DPA1*0103 -DPB1*0201 haplotype (Pc<0.02) is associated with protection from both grade II and III severe fibrosis. There was no association between HLA-B DNA haplotypes and the disease. These findings indicate that the HLA-class II molecules play a role in preventing or promoting fibrotic liver change after deposition with Schistosome eggs. Moreover, a tendency was observed within the HLA class II genes for the HLA-DR-DQ alleles to be associated with protection against early changes in liver fibrosis, whereas HLA-DP alleles were associated with protection from the late phase of fibrosis or severe hepatosplenic schistosomiasis.

Alleles↗

Stable restoration of the sarcoglycan complex in dystrophic muscle perfused with histamine and a recombinant adeno-associated viral vector.

Limb-girdle muscular dystrophies 2C-F represent a family of autosomal recessive diseases caused by defects in sarcoglycan genes. The cardiomyopathic hamster is a naturally occurring model for limb-girdle muscular dystrophy caused by a primary deficiency in delta-sarcoglycan. We show here that acute sarcolemmal disruption occurs in this animal model during forceful muscle contraction. A recombinant adeno-associated virus vector encoding human delta-sarcoglycan conferred efficient and stable genetic reconstitution in the adult cardiomyopathic hamster when injected directly into muscle. A quantitative assay demonstrated that vector-transduced muscle fibers are stably protected from sarcolemmal disruption; there was no associated inflammation or immunologic response to the vector-encoded protein. Efficient gene transduction with rescue of the sarcoglycan complex in muscle fibers of the distal hindlimb was also obtained after infusion of recombinant adeno-associated virus into the femoral artery in conjunction with histamine-induced endothelial permeabilization. This study provides a strong rationale for the development of gene therapy for limb-girdle muscular dystrophy.

Animals↗

The pharmacokinetics of lamivudine in healthy Chinese subjects.

AIMS: The purpose of this study was to investigate the pharmacokinetics of daily oral doses of lamivudine administered to healthy Chinese subjects for 1 week. METHODS: Twenty-four subjects were enrolled, 12 males and 12 females, all between the ages of 18 and 40 years. After an overnight fast, all subjects received a single oral dose of 100 mg lamivudine. Blood was obtained before lamivudine administration and at regular intervals to 24 h post dose. Subsequent doses were given once daily for a total of 7 days. On the last day another full pharmacokinetic profile was obtained to 24 h postdose. Timed urine collections were performed for all subjects on day 1 only. Pharmacokinetic parameters were calculated by using standard non compartmental techniques. RESULTS: Lamivudine was well absorbed in all subjects (tmax 1 h). On day 1 and day 7 the overall geometric mean Cmax was 1304 and 1385 ng ml-1, and AUC(0,24h) was 4357 and 4353 ng ml-1 h, respectively. On average 78% of the lamivudine dose was recovered in urine as parent compound. Pharmacokinetic parameters were very similar between male and female subjects, between day 1 and day 7 and in comparison with data obtained in many other pharmacokinetic studies. CONCLUSIONS: This study demonstrated that the pharmacokinetics of lamivudine are essentially identical between Chinese and Caucasian subjects, and between males and females. It confirms 100 mg lamivudine is an appropriate dose for use in Chinese patients, providing adequate exposure for optimal antiviral effect.

Adult↗

Growth inhibition of psoriatic keratinocytes by quinazoline tyrosine kinase inhibitors.

Psoriasis is characterized by hyperproliferation of keratinocytes associated with an inflammatory infiltrate in the epidermis. Among factors which may be related to hyperplasia of psoriatic keratinocytes is the persistent autocrine stimulation of the epidermal growth factor receptor (EGFR) by transforming growth factor-alpha. Owing to the pivotal role of the EGFR in driving the growth of human psoriatic keratinocytes, we examined two selective inhibitors of EGFR kinase activity: 4-(3-bromophenylamino)-6, 7-dimethoxyquinazoline (AG1517/SU5271) and 4-(3-chlorophenylamino)-6, 7-dimethoxyquinazoline (AG1478) on psoriatic keratinocytes. SU5271 potently inhibits ligand-induced autophosphorylation of EGFR, and downstream signal transduction events, including DNA replication and cell cycle progression. SU5271, at micromolar concentrations, inhibited the proliferation of keratinocytes isolated from psoriatic lesions in excellent correlation with its EGFR kinase inhibitory activity in these cells. Biologically active concentrations of SU5271 penetrated human cadaver skin, suggesting that this compound is a strong candidate as an antipsoriatic agent.

Animals↗

EGF promotes development of a differentiated trophoblast phenotype having c-myc and junB proto-oncogene activation.

Human placental cytotrophoblast cells differentiate by a process of fusion into a syncytium. This process is stimulated by EGF but also occurs spontaneously at a slower rate in cultured cytotrophoblast cells. To determine nuclear proto-oncogene changes mediating these events, c-myc, c-fos, c-jun and junB were measured in spontaneously differentiating cells and in cells exposed to EGF. c-myc showed a transient rise in expression at 4-8 h with augmented expression by EGF, occurring even in the absence of serum or attachment. c-myc and c-jun declined during culture, but c-fos and particularly junB showed increased expression by day 3 with marked responses to EGF stimulation. Syncytia induced to form by EGF exposure for 48 h demonstrated marked junB expression after rechallenge with 40 min EGF exposure, but negligible responses of c-fos and c-jun. c-myc showed increased expression after 6 h EGF exposure throughout the culture period and in syncytia. The results indicate EGF promotes a syncytial phenotype characterized by c-fos and junB expression during syncytial formation. EGF continues to elicit junB and c-myc responsiveness in more mature syncytium, indicative of continued EGF actions which may include acting as a survival factor, as an hCG secretagogue, and as an inducer of continued development of the syncytium.

Cell Adhesion↗

Outpatient minimally invasive parathyroidectomy: a combination of sestamibi-SPECT localization, cervical block anesthesia, and intraoperative parathyroid hormone assay.

BACKGROUND: Despite the high cure rate and low morbidity of bilateral neck exploration for primary hyperparathyroidism, there is a movement toward minimizing the process in terms of incision, cost, extent of exploration, and length of hospital stay, while maintaining excellent outcomes. METHODS: Between March and November 1998, 33 patients with primary hyperparathyroidism underwent minimally invasive parathyroidectomy. All had preoperative sestamibi-SPECT scans suggesting a single adenoma, underwent anterior cervical block anesthesia by the surgeon, and were explored through a 1- to 4-cm incision. Intraoperative parathyroid hormone assays were performed before and 5 to 10 minutes after parathyroid resection. Outcomes were compared with those of 184 consecutive patients who underwent bilateral parathyroid exploration under general anesthesia by the same surgeon between August 1990 and May 1996. RESULTS: The mean age of the patients undergoing minimally invasive parathyroidectomy was 61 +/- 2 years, and 24 of the 33 patients were women. Thirty (91%) had resection of a single adenoma under regional anesthesia; 26 of these were done as outpatient procedures. Three patients underwent conversion to general anesthesia for bilateral exploration and were found to have multigland disease (two double adenomas, one hyperplasia). All 33 patients were normocalcemic postoperatively. There was no morbidity. When the minimally invasive parathyroidectomy and bilateral parathyroid exploration groups were compared, they were found to be similar with respect to age, preoperative calcium and parathyroid hormone levels, cause of primary hyperparathyroidism, weight of resected glands, cure rates, and morbidity. However, the minimally invasive parathyroidectomy group had a significantly shorter length of hospital stay (0.3 +/- 0.2 vs 1.8 +/- 0.1 days, P < .001) and lower costs ($3174 +/- $386 vs $6328 +/- $292, P < .001). CONCLUSIONS: Minimally invasive parathyroidectomy is a safe, cost-effective alternative to bilateral exploration and may be the procedure of choice for select patients with primary hyperparathyroidism.

Adenoma↗

Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women.

BACKGROUND: Osteoporosis and related fractures will be growing public health problems as the population ages. It is therefore of great importance to identify modifiable risk factors. OBJECTIVE: We investigated associations between dietary components contributing to an alkaline environment (dietary potassium, magnesium, and fruit and vegetables) and bone mineral density (BMD) in elderly subjects. DESIGN: Dietary intake measures were associated with both cross-sectional (baseline) and 4-y longitudinal change in BMD among surviving members of the original cohort of the Framingham Heart Study. Dietary and supplement intakes were assessed by food-frequency questionnaire, and BMD was measured at 3 hip sites and 1 forearm site. RESULTS: Greater potassium intake was significantly associated with greater BMD at all 4 sites for men and at 3 sites for women (P < 0.05). Magnesium intake was associated with greater BMD at one hip site for both men and women and in the forearm for men. Fruit and vegetable intake was associated with BMD at 3 sites for men and 2 for women. Greater intakes of potassium and magnesium were also each associated with less decline in BMD at 2 hip sites, and greater fruit and vegetable intake was associated with less decline at 1 hip site, in men. There were no significant associations between baseline diet and subsequent bone loss in women. CONCLUSION: These results support the hypothesis that alkaline-producing dietary components, specifically, potassium, magnesium, and fruit and vegetables, contribute to maintenance of BMD.

Aged↗

Small bowel metastases of malignant melanoma: palliative effect of surgical resection.

Malignant melanoma shows an unusual predilection to metastasize to the small intestine. Three patients with malignant melanoma involving the small bowel are reported. One patient was operated on for small bowel obstruction and the other two for gastrointestinal bleeding. Two patients remained well 6 and 2 years, respectively, after surgery. One patient died of metastatic melanoma 4 years post-operation. Metastatic melanoma in the small bowel should be suspected in any patient with a previous history of malignant melanoma who develops GI symptoms or chronic blood loss. Surgical treatment was the first choice; the prognosis after surgical resection was much better than for other organ metastases or simultaneous metastases of the small bowel and other organs.

Adult↗

Update on interconversions of vitamin B-6 with its coenzyme.

Biosynthesis of pyridoxal 5'-phosphate (PLP) depends upon the relatively specific action of two consecutive enzymes, viz. pyridoxal (pyridoxine, pyridoxamine) kinase and pyridoxine (pyridoxamine) phosphate oxidase. Less specific phosphatases catalyze hydrolyses of the 5'-phosphates of the vitamers pyridoxal, pyridoxamine, and pyridoxine. From the recognition a generation ago of these processes by which the three forms of vitamin B-6 and their 5'-phosphates are interconverted, more recent studies have provided a fairly sophisticated understanding of the molecular characteristics of the enzymes involved. The evolutionary retention of homologous portions of pyridoxal kinase in humans as well as bacteria and the most recent finding of a highly conserved region of the pyridoxine (pyridoxamine) phosphate oxidase, also from both prokaryotic and eukaryotic organisms, emphasize the importance of these catalysts in the formation of a coenzyme that is essential for most organisms. Both kinase and oxidase involved in B-6 metabolism are potential targets for pharmacologic agents.

Amino Acid Sequence↗

Carotenoid intakes, assessed by dietary questionnaire, are associated with plasma carotenoid concentrations in an elderly population.

High intakes of fruits and vegetables and of carotenoids are associated with a lower risk for a variety of chronic diseases. It is therefore important to test the validity of dietary questionnaires that assess these intakes. We compared intakes of five carotenoids, as calculated from responses to the Willett 126-item food-frequency questionnaire, with corresponding biochemical measures. Subjects included 346 women and 201 men, aged 67-93 y, in the Framingham Heart Study. Unadjusted correlations were higher among women than men as follows: alpha-carotene 0.33 and 0.18, beta-carotene, 0.36 and 0.25; beta-cryptoxanthin, 0.44 and 0.32; lycopene, 0.35 and 0.21; and lutein + zeaxanthin, 0.27 and 0.10, respectively. Adjustment for age, energy intake, body mass index (BMI, kg/m2), plasma cholesterol concentrations and smoking reduced the gender differences, respectively, to the following: alpha-carotene 0.30 and 0.28; beta-carotene, 0.34 and 0.31; beta-cryptoxanthin, 0.45 and 0.36; lycopene, 0.36 and 0.31; and lutein + zeaxanthin, 0.24 and 0.14. Plots of adjusted mean plasma carotenoid concentration by quintile of respective carotenoid intake show apparent greater responsiveness among women, compared with men, to dietary intake of alpha- and beta-carotene and beta-cryptoxanthin, but similar blood-diet relationships for lycopene and lutein + zeaxanthin. Reported daily intake of fruits and vegetables correlated most strongly with plasma beta-cryptoxanthin and beta-carotene among women and with plasma alpha- and beta-carotene among men. With the exception of lutein + zeaxanthin, this dietary questionnaire does provide reasonable rankings of carotenoid status among elderly subjects, with the strongest correlations for beta-cryptoxanthin. Appropriate adjustment of confounders is necessary to clarify these associations among men.

Aged↗

Anal ultrasound predicts the response to nonoperative treatment of fecal incontinence in men.

OBJECTIVE: To assess the etiology, treatment, and utility of anal ultrasound in men with fecal incontinence and to review the outcomes of conservative (nonoperative) treatment. SUMMARY BACKGROUND DATA: The etiology of fecal incontinence in women is almost exclusively from obstetric or iatrogenic surgical injuries resulting in damage to the anal sphincters and/or pudendal nerves. Corresponding data on men with fecal incontinence are sparse. METHODS: Between January 1995 and January 1998, 37 men with fecal incontinence were evaluated in the John Radcliffe Hospital anorectal ultrasound unit. Their clinical histories, anal ultrasound results, anorectal physiology studies, and responses to conservative therapy were reviewed. RESULTS: Median age was 57 years. Major incontinence was present in 27% of the patients. Anal ultrasound localized anal sphincter damage in nine patients, and the characteristics of these nine patients with sphincter damage were then compared with the remaining 28 without sphincter damage. Prior anal surgery was more common in patients with sphincter damage. Hemorrhoids were more common in patients without sphincter damage. Anorectal physiology studies revealed significantly lower mean maximum resting and squeeze pressures in patients with sphincter damage, confirming poor sphincter function. With 92% follow-up, patients without sphincter damage were more likely to improve with nonoperative therapy. CONCLUSIONS: Anal ultrasound is extremely useful in the evaluation of fecal incontinence in men. Unlike women, the majority of men do not have a sphincter defect by anal ultrasound, and conservative management is usually successful in these patients. In contrast, in men with anal sphincter damage, almost all of these defects resulted from previous anal surgery. Conservative management rarely is successful in these cases, and surgical repair of the anal sphincter may be indicated. Therefore, because the presence or absence of sphincter damage on anal ultrasound usually predicts the response to nonoperative treatment, anal ultrasound should be used to guide the initial management of men with fecal incontinence.

Adult↗