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Biomedical subjects

J C Li

Publications and source records attributed to J C Li.

At least 19 recordsLinked to original sources
PubMed1999

Optimal proliferation of a hematopoietic progenitor cell line requires either costimulation with stem cell factor or increase of receptor expression that can be replaced by overexpression of Bcl-2.

In vitro proliferation of hematopoietic stem cells requires costimulation by multiple regulatory factors whereas expansion of lineage-committed progenitor cells generated by stem cells usually requires only a single factor. The distinct requirement of factors for proliferation coincides with the differential temporal expression of the subunits of cytokine receptors during early stem cell differentiation. In this study, we explored the underlying mechanism of the requirement of costimulation in a hematopoietic progenitor cell line TF-1. We found that granulocyte-macrophage colony-stimulating factor (GM-CSF) optimally activated proliferation of TF-1 cells regardless of the presence or absence of stem cell factor (SCF). However, interleukin-5 (IL-5) alone sustained survival of TF-1 cells and required costimulation of SCF for optimal proliferation. The synergistic effect of SCF was partly due to its anti-apoptosis activity. Overexpression of the IL-5 receptor alpha subunit (IL5Ralpha) in TF-1 cells by genetic selection or retroviral infection also resumed optimal proliferation due to correction of the defect in apoptosis suppression. Exogenous expression of an oncogenic anti-apoptosis protein, Bcl-2, conferred on TF-1 cells an IL-5-dependent phenotype. In summary, our data suggested SCF costimulation is only necessary when the expression level of IL5Ralpha is low and apoptosis suppression is defective in the signal transduction of IL-5. Expression of Bcl-2 proteins released the growth restriction of the progenitor cells and may be implicated in leukemia formation.

Cell Differentiation↗
PubMed1998

Quantification of prostaglandin D synthetase in cerebrospinal fluid: a potential marker for brain tumor.

Prostaglandin D synthetase (PGD-S; prostaglandin-H2 D-isomerase, EC 5,3,99,2), a 30 kDa glycoprotein also known as beta-trace protein that catalyzes the formation of prostaglandin D2 (PGD2) from PGH2, was purified to apparent homogeneity from human cerebrospinal fluid (CSF) using a two-step procedure involving HPLC on a Vydac C8 reversed-phase column and high performance electrophoresis chromatography (HPEC) using a 10% T SDS-polyacrylamide gel. The purity of PGD-S isolated from CSF was confirmed by silver stained SDS-polyacrylamide gel and direct protein microsequencing (NH2-APEAQVSVQPNFQ). A highly specific polyclonal antibody was prepared against this protein for immunoassay development. Using an ELISA, it was found that the concentration of PGD-S in CSF did not alter significantly in different pathological conditions of the central nervous system (CNS). These include dementia (n = 9), hydrocephalus (n = 4), neuropathy (n = 11), optic neuritis (n = 4), multiple sclerosis (n = 11), and demyelinating syndrome (n = 11), when compared to normal individuals (n = 12); however, the level of PGD-S in the CSF obtained from patients with brain tumor (n = 11), was reduced by as much as 2-fold when compared to control samples (n = 12) illustrating PGD-S is a potentially useful marker for brain tumor.

Amino Acid Sequence↗
PubMed1998

mcl-1 is an immediate-early gene activated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway and is one component of the GM-CSF viability response.

mcl-1, a bcl-2 family member, was originally identified as an early gene induced during differentiation of ML-1 myeloid leukemia cells. In the present study, we demonstrate that Mcl-1 is tightly regulated by the granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling pathway. Upon deprivation of survival factor from TF-1 myeloid progenitor cells, Mcl-1 levels quickly dropped prior to visible detection of apoptosis of these cells. Upon restimulation of these deprived cells with GM-CSF, the mcl-1 mRNA was immediately induced and its protein product was accordingly resynthesized. Analysis with Ba/F3 cells expressing various truncation mutants of the GM-CSF receptor revealed that the membrane distal region between amino acids 573 and 755 of the receptor beta chain was required for mcl-1 induction. Transient-transfection assays with luciferase reporter genes driven by various regions of the mcl-1 promoter demonstrated that the upstream sequence between -197 and -69 is responsible for cytokine activation of the mcl-1 gene. Overexpression of mcl-1 delayed but did not completely prevent apoptosis of cells triggered by cytokine withdrawal. Its down regulation by antisense constructs overcame, at least partially, the survival activity of GM-CSF and induced the apoptosis of TF-1 cells. Taken together, these results suggest that mcl-1 is an immediate-early gene activated by the cytokine receptor signaling pathway and is one component of the GM-CSF viability response.

Amino Acid Sequence↗
PubMed1997

Rabbit sex hormone binding globulin: primary structure, tissue expression, and structure/function analyses by expression in Escherichia coli.

Sex hormone binding globulin (SHBG) is a homodimeric plasma protein found in mammals that binds sex steroids with high affinity and regulates their bioavailability. The protein is identical in structure and properties to the androgen binding protein (ABP) found in the male reproductive tract. We have isolated a 1245-base pair rabbit SHBG cDNA encoding a reading frame for a signal peptide followed by a protein of 367 amino acids, which shares 79.0, 68.1 and 63.2% amino acid identity with the corresponding human, rat and mouse proteins respectively. Northern blot and hot-nested PCR analyses indicated that rabbit SHBG is produced from a 1.6 kilobase mRNA in the liver of both sexes and in the testis. The rabbit SHBG cDNA was inserted into pGEX-1 lambda T for expression of a glutathione S-transferase/SHBG fusion protein in Escherichia coli. The bacterial product bound 5 alpha-dihydrotestosterone (DHT) in the same manner as the corresponding protein in serum. The dissociation constants (Kd) for rabbit and human SHBGs produced in E. coli were 11.1 +/- 1.1 nM and 2.1 +/- 0.6 nM respectively, and rabbit SHBG formed a less stable protein-steroid complex (t1/2 = 5 min) than human SHBG (t1/2 > 60 min). Unlike human SHBG, rabbit SHBG does not bind estradiol with high affinity. To aid in the identification of differences in the sequences of rabbit and human SHBG, which determine species differences in steroid-binding affinity and specificity, chimeras containing the 5'-terminal half of SHBG from one species and 3'-terminal half of SHBG from the other species were constructed and expressed. It was found that the chimeric proteins assumed similar steroid-binding affinity and specificity as the wild-type proteins when the amino (N)-terminal half of SHBG was derived from the same species. Replacement of the carboxyl (C)-terminal half of rabbit SHBG by the corresponding region of the human molecule increased the integrity of its steroid-protein complex. This supports the concept that amino acids within the N-terminal half of SHBG constitute the steroid-binding domain while the C-terminal half of the molecule may provide structural stability to the protein and its steroid-binding site.

Amino Acid Sequence↗
PubMed1997

CP-225,917 and CP-263,114, novel Ras farnesylation inhibitors from an unidentified fungus. I. Taxonomy, fermentation, isolation, and biochemical properties.

During the course of our screening for squalene synthase inhibitors and Ras farnesylation inhibitors, a novel fungal culture was discovered to produce two structurally unique compounds, CP-225,917 and CP-263,114, as well as zaragozic acid A (squalestatin I). The two compounds are characterized by a bicyclo[4.3.1]dec-1,6-diene core plus two extended alkyl chains. CP-225,917 and CP-263,114 inhibit Ras farnesyl transferase from rat brain with IC50 values of 6 microM and 20 microM, respectively. CP-225,917 inhibits squalene synthase with an IC50 value of 43 microM and CP-263,114 with an IC50 of 160 microM. The producing organism, though not fully classified, exhibits the characteristics of a sterile Phoma species.

Alkyl and Aryl Transferases↗
PubMed1997

[Roles of intercellar Ca2+ and protein kinase C played in tissue factor pathway inhibitor and tissue factor expression in human umbilic vein endothelial cells].

The purpose of the present study was to elucidate the roles that protein kinase C (PKC) and calcium played in the tissue factor (TF) synthesis and tissue factor pathway inhibitory (TFPI) release in human umbilic vein endothelial cells (HUVEC). A23187 was used to represent calcium ionophore and phorbol 12-myristate 13-acetate (PMA) as that of PKC activator. TF activity in the lysed HUVEC was measured using one stage clotting assay. TFPI activity in the conditioned medium of HUVEC was assessed by the two-step chromogenic method. The results showed that the TF activities in A23187, PMA and A23187 + PMA groups were remarkably higher (P < 0.01) than that in control. Among the three treated groups, the TF activities in both A23187 group and A23187 + PMA group were lower than that in the PMA group (P < 0.05), but the difference between the former two groups was statically insignificant (P > 0.05). In contrast to the control group, the TFPI activity in the A23187 group was not statistically different (P > 0.05). However, the TFPI activities in the PMA group and the A23187 + PMA group were markedly higher than those in the control group and the A23187 group (P < 0.01). These findings indicate that PKC and calcium ion promote TF synthesis in HUVEC but the effect of the former is stronger than that of the latter, and that the release of TFPI from HUVEC is facilitated by PKC and not significantly affected by calcium ion.

Calcium↗
PubMed1995

Mastoid oscillation: a critical factor for success in canalith repositioning procedure.

The canalith repositioning procedure has recently gained controversial recognition as a treatment for benign paroxysmal positional vertigo. Some authors contend that the canalith repositioning maneuver is no more effective than no treatment at all. Unfortunately, its technique has not been uniformly applied and its outcomes have not been uniformly assessed. I have found the use of mastoid oscillation to be critical in the success of this procedure. Another important factor is the time interval between diagnosis and relief of symptoms. Because it is well known that benign paroxysmal positional vertigo can spontaneously resolve after many months, the time frame for comparison should be short. A 1-week time interval was chosen for study purposes. Sixty patients were randomly assigned to three initial groups. The control group (n = 23) was not given any treatment. A second group (n = 27) was given treatment with the canalith repositioning maneuver with mastoid vibration. A third group (n = 10) was assigned to receive the canalith repositioning maneuver without mastoid vibration. Resolution was defined as no symptoms and negative Dix-Hallpike test results. The results showed that none of the control group's symptoms resolved completely in 1 week. Although 60% of those who received the canalith repositioning maneuver without mastoid vibration felt improved, none was free of nystagmus. An overwhelming 92% of those who received the canalith repositioning maneuver with mastoid vibration felt improved, and 70% were free of rotatory nystagmus after only one treatment. A review of all patients diagnosed with benign paroxysmal positional vertigo and treated with the canalith repositioning maneuver with mastoid vibration was also undertaken. In a series of 67 patients with a minimum of four weeks of follow-up, only two have not responded to the canalith repositioning maneuver, yielding a 97% rate of symptom control.

Humans↗
PubMed1995

One-dimensional V-Scope analysis of habituation to simulated cross-country skiing.

Responses to simulated cross-country skiing were measured using the V-Scope, a new telemetric ultrasound motion monitor. Ten young male adults performed a total of 45 minutes of distributed practice on a Nordic-Track ski simulator. Over a period of three 15-minute sessions cadence and velocity were unchanged. Step and stride lengths decreased significantly (p < 0.05) after the first 15-minute session and then remained unchanged. There were no left-right limb differences across all sessions indicating a normal gait. Response variability in velocity, step lengths and stride length was dramatically reduced after the first exposure period. This study demonstrates that the V-Scope system is a useful motion analysing device and, on the basis of the data presented in this preliminary investigation, at least two 15-minute habituation sessions are required for initial habituation to simulated cross-country skiing.

Acceleration↗
PubMed1995

Modified retrosigmoid approach: use for selected acoustic tumor removal.

The authors have used a modified retrosigmoid (suboccipital) approach for removal of acoustic tumors in selected patients who have good preoperative hearing and whose tumor does not reach the brain stem or extend to the lateral third of the internal auditory canal. This report presents the surgical technique and results for 15 acoustic neuromas removed by members of the House Ear Clinic between 1986 and 1991 using this approach. The technique differs importantly from the standard suboccipital approach. A mastoidectomy with decompression of the sigmoid sinus allows forward retraction of the sigmoid sinus, enabling tumor removal without cerebellar retraction. Also, replacement of the craniotomy flap prevents adherence to the dura of the scalp, which may prevent postoperative headaches. Tumor size ranged from 0.8 cm to 4.0 cm (mean, 1.9 cm). At 1 year or more postoperative, 13 of the 14 patients with follow-up available had a House-Brackmann (H-B) facial nerve grade I, and one patient had H-B grade II. Three patients retained good hearing ( < or = 30 dB SRT and > or = 70% speech discrimination) postoperatively, and 57% retained at least measurable hearing. For a patient with good preoperative hearing and a tumor that is medially based, involving the cerebellopontine angle but not extending to the brain stem or the lateral end or the internal auditory canal, the authors will continue to use the retrosigmoid approach for tumor removal.

Adult↗
PubMed1994

[Ultrasonographic study on primary hyperparathyroidism: evaluation of B-mode and color Doppler ultrasonography in localization].

Seventy six patients with primary hyperparathyroidism were studied systematically by B-mode ultrasonography (BUS) and color Doppler flow imaging (CDFI). The sensitivity to the patients was 72%, specificity 92%, accuracy 87%, positive predictive value 69%, and negative predictive value 92%. The diagnostic efficiency was the highest in the parathyroid adenomas in normal position. By comparing the diagnostic efficiency of BUS with CDFI, we found that the sensitivity was significantly different (P < 0.05) and the accuracy greatly significantly different (P < 0.01). The accuracy of CDFI was higher than that of BUS. We discussed the value of BUS in localization in the parathyroid lesions and discrimination between the various kinds of parathyroid lesions. In addition, ectopic parathyroid lesions, hyperparathyroid crisis, and comparison between various imaging examinations were also studied. It is suggested that the diagnostic level of BUS and CDFI in primary hyperparathyroidism be improved.

Adenoma↗
PubMed1994

Myocardial protection of cold crystalloid and warm blood cardioplegia. A comparative study.

Twenty patients undergoing open-heart valvular operations were divided randomly into two groups. Intermittent perfusion of cold crystalloid (St. Thomas Hospital solution) with hypothermic cardiopulmonary bypass (CPB) in the hypothermic group and continuous administration of warm blood cardioplegia with normothermic CPB in the normothermic group were used respectively. The results of warm blood cardioplegia were superior to those of cold crystalloid. 70% of patients treated with the warm technique had spontaneous return of normal sinus rhythm shortly after removal of the aortic cross-clamp, compared with only 10% of the hypothermic group (P < 0.05). The extracorporeal support time from releasing of aortic clamp to the weaning of CPB was significantly shorter in the normothermic group (33.50 +/- 3.78 min vs. 25.00 +/- 4.64 min, P < 0.05). The postoperative ventilation support time was also much shorter than that of the hypothermic group (19.84 +/- 1.11 h vs. 38.98 +/- 16.55 h, P < 0.05). More atrial beating occurred in the normothermic group (80% vs. 20%, P < 0.05) during aortic clamping, and it is showed that continuous warm blood cardioplegia might not efficiently prevent the atrium from damage.

Adult↗
PubMed1994

[A report of 29 cases of silicosis complicated with mediastinal emphysema].

The experience to treat SCME in the past twenty-three years was reported. The method of upper mediastinotomy for saving the patients was introduced. The authors suggested control of the pulmonary infection and appropriate treatment of pneumothorax are important in preventing the occurrence of mediastinal emphysema.

Adult↗
PubMed1993

The concept of transtympanic injection of fibrin caulk.

Cerebrospinal fluid otorhinorrhea after basilar skull trauma poses a difficult management problem. When conservative techniques fail, more aggressive neurosurgical and otologic procedures are required to control cerebrospinal fluid leakage. We assessed a less invasive method for the repair of traumatic cerebrospinal fluid fistulas. Thirty-one adult Sprague-Dawley rats were used to develop an animal model for the treatment of cerebrospinal fluid leakage. A fistula was created by removing a thin plate of bone from the superior aspect of the rat bulla. The bulla was then plugged with a transtympanic injection of fibrin caulk. Otoscopic and histologic data were collected at selected intervals. Transtympanic injection of fibrin caulk failed to alter significantly the rate of healing of cerebrospinal fluid fistulas. Coagulum retraction, rapid fibrinolysis, and other reasons for failure are explored.

Animals↗
PubMed1993

Endolymphatic sac tumors: radiologic appearance.

PURPOSE: To evaluate the radiologic appearance of endolymphatic sac tumors (ELSTs). MATERIALS AND METHODS: Four patients with ELST underwent computed tomography (CT), and two of the four also underwent magnetic resonance (MR) imaging. Their radiologic studies were reviewed for characteristic findings of ELST. RESULTS: Retrolabyrinthine bone destruction was centered at the external aperture of the vestibular aqueduct in all four patients. CT showed irregular bone margins and prominent intratumoral bone in all four patients. At MR imaging, one tumor was almost homogeneous and isointense to gray matter with T1 weighting, and the other was heterogeneous and contained hyper-, hypo-, and isointense foci with T1 and T2 weighting. CONCLUSION: These radiologic changes may help distinguish ELSTs from other tumors of the temporal bone and posterior fossa.

Adenocarcinoma↗
PubMed1993

Reclassification of aggressive adenomatous mastoid neoplasms as endolymphatic sac tumors.

The emerging concept that aggressive adenomatous tumors of the temporal bone arise from the endolymphatic sac and constitute a distinct clinicopathologic entity merits wider recognition. These tumors share a common clinical pattern and exhibit consistent imaging and histopathologic features. Endolymphatic sac tumors (ELSTs) have been mistaken for other neoplasms such as paragangliomas, adenomatous tumors of mixed histology, ceruminomas, and choroid plexus papillomas. A review of the literature shows similarities among case studies of these aggressive adenomatous lesions. An analysis of the data supports the endolymphatic sac as an origin for these tumors. This report also presents an additional case of a less differentiated variant of this rare but important clinicopathologic entity.

Adenoma↗
PubMed1993

[Detecting respiratory syncytial virus in respiratory epithelial cells in adult patients by electron microscopy and immune electron microscopy].

In order to evaluate the value of electron microscopy (EM) in diagnosing respiratory syncytial virus (RSV) infection in adults, the exfoliated cells from nasopharynx of 97 RSV positive patients were examined by EM and the gold labelling technique for immune electron microscopy. The viral particles with RSV features were found at the surface of the exfoliated cells only in a few samples by EM, and the specific gold labelling were observed in the immune electron microscopy (IEM). The results showed that RSV is one of the causative agents for adult respiratory infection.

Adolescent↗
PubMed1992

Repair of DNA damage induced by oxygen radicals in human non-proliferating and proliferating lymphocytes.

Repair of DNA lesions induced by oxygen radicals, generated by xanthine/xanthine oxidase (X/XO), was studied in human peripheral blood lymphocytes and in PHA-stimulated proliferating lymphocytes from 4 healthy subjects. The lesions included DNA-strand breaks (SSB) and other lesions that are converted to SSB under alkaline conditions. The frequencies of SSB were estimated by fluorometric analysis of DNA unwinding. Maximum production of SSB occurred within 10 min of incubation with X/XO at 22 degrees C; with 0.5 mM or higher concentrations of xanthine; and with 0.1-0.5 units/ml of xanthine oxidase. Proliferating lymphocytes repaired X/XO-induced SSB about 4 times more rapidly than lymphocytes. Lymphocytes repaired X/XO-induced SSB more slowly than SSB caused by gamma-radiation. These findings are consistent with the evidence that a number of DNA-repair enzymes have greater activity in proliferating cells than in resting cells. These findings also support the view that there are differences between the DNA damage due to oxygen radicals and that due to ionizing radiation.

DNA↗