Biomedical subjects

A Tsang

Publications and source records attributed to A Tsang.

At least 19 recordsLinked to original sources

PubMed2004

Ischemic preconditioning protects by activating prosurvival kinases at reperfusion.

Pharmacological activation of the prosurvival kinases Akt and ERK-1/2 at reperfusion, after a period of lethal ischemia, protects the heart against ischemia-reperfusion injury. We hypothesized that ischemic preconditioning (IPC) protects the heart by phosphorylating the prosurvival kinases Akt and ERK-1/2 at reperfusion. In isolated perfused Sprague-Dawley rat hearts subjected to 35 min of lethal ischemia, the phosphorylation states of Akt, ERK-1/2, and p70 S6 kinase (p70S6K) were determined after 15 min of reperfusion, and infarct size was measured after 120 min of reperfusion. IPC induced a biphasic response in Akt and ERK-1/2 phosphorylation during the preconditioning and reperfusion phases after the period of lethal ischemia. IPC induced a fourfold increase in Akt, ERK-1/2, and p70S6K phosphorylation at reperfusion and reduced the infarct risk-to-volume ratio (56.9 +/- 5.7 and 20.9 +/- 3.6% for control and IPC, respectively, P < 0.01). Inhibiting the IPC-induced phosphorylation of Akt, ERK-1/2, and p70S6K at reperfusion with the phosphatidylinositol 3-kinase (PI3K) inhibitor LY-294002 or the MEK-1/2 inhibitor PD-98059 abrogated IPC-induced protection (46.3 +/- 5.8, 49.2 +/- 4.0, and 20.9 +/- 3.6% for IPC + LY-294002, IPC + PD-98059, and IPC, respectively, P < 0.01), demonstrating that the phosphorylation of these kinases at reperfusion is required for IPC-induced protection. In conclusion, we demonstrate that the reperfusion phase following sustained ischemia plays an essential role in mediating IPC-induced protection. Specifically, we demonstrate that IPC protects the heart by phosphorylating the prosurvival kinases Akt and ERK-1/2 at reperfusion.

Animals↗

PubMed2003

The management of retroperitoneal liposarcoma with synchronous intra-duodenal sarcoma.

Intra-abdominal (as opposed to extremity or limb and limb-girdle) soft tissue sarcomas (STS) are rare and account for less than 1% of all diagnosed neoplasms. These tumours are usually associated with a poor prognosis and are often locally invasive and metastatic at the time of presentation. Retroperitoneal sarcomas with synchronous or metachronous different histological types are rare and intra-duodenal sarcomas extremely unusual. A case of a giant retroperitoneal STS weighing approximately 15 kg consisting of two histologically different types is presented. Intra-duodenal involvement with sarcoma was found intra-operatively. We discuss the management of this condition in the context of an illustrative case in our recent experience.

Adult↗

PubMed2001

RasG regulates discoidin gene expression during Dictyostelium growth.

Activated rasG, rasG(G12T), was expressed in Dictyostelium cells under the control of the folate-repressible discoidin promoter (pVEII-rasG(G12T)) and found to have a unique pattern of expression when cells were transferred to folate-deficient media: an initial increase of RasG(G12T) resulting from the removal of folate, followed by a rapid decline while cells were still in the early exponential phase of growth. Discoidin levels were considerably lower and declined more rapidly in the pVEII-rasG(G12T) transformant than they did in the wild type, suggesting that RasG(G12T) represses discoidin expression. This was independently confirmed by placing the rasG(G12T) gene under the control of the ribonucleotide reductase (rnrB) promoter. Exposure of cells to 10 mM methyl methanesulfonate (MMS) rapidly generated RasG(G12T) and this was accompanied by an equally rapid decrease in discoidin mRNA levels. rasG null cells also contained decreased levels of discoidin under all conditions tested, indicating that RasG is essential for optimum discoidin expression. However, rasG null cells showed normal regulation of discoidin expression in response to PSF, CMF, folate, bacteria, and axenic media, indicating that RasG is not necessary for any of these responses. These results reveal a role for RasG in regulating discoidin gene expression and add a further level of complexity to the regulation of the discoidin promoter.

Animals↗

PubMed2001

Involvement of a triton-insoluble floating fraction in Dictyostelium cell-cell adhesion.

We have isolated and characterized a Triton-insoluble floating fraction (TIFF) from Dictyostelium. Ten major proteins were consistently detected in TIFF, and six species were identified by mass spectrometry as actin, porin, comitin, regulatory myosin light chain, a novel member of the CD36 family, and the phospholipid-anchored cell adhesion molecule gp80. TIFF was enriched with many acylated proteins. Also, the sterol/phospholipid ratio of TIFF was 10-fold higher than that of the bulk plasma membrane. Immunoelectron microscopy showed that TIFF has vesicular morphology and confirmed the association of gp80 and comitin with TIFF membranes. Several TIFF properties were similar to those of Dictyostelium contact regions, which were isolated as a cytoskeleton-associated membrane fraction. Mass spectrometry demonstrated that TIFF and contact regions shared the same major proteins. During development, gp80 colocalized with F-actin, porin, and comitin at cell-cell contacts. These proteins were also recruited to gp80 caps induced by antibody cross-linking. Filipin staining revealed high sterol levels in both gp80-enriched cell-cell contacts and gp80 caps. Moreover, sterol sequestration by filipin and digitonin inhibited gp80-mediated cell-cell adhesion. This study reveals that Dictyostelium TIFF has structural properties previously attributed to vertebrate TIFF and establishes a role for Dictyostelium TIFF in cell-cell adhesion during development.

Animals↗

PubMed2001

Two distinct receptors mediate nonopsonic phagocytosis of different strains of Pseudomonas aeruginosa.

Complement receptor 3 (CR3) mediates both opsonic and nonopsonic phagocytosis of bacteria. Leukocyte adhesion deficiency (LAD) allows for the study of CR3-dependent phagocyte-bacterial ingestion, since LAD phagocytes do not express this receptor. Phagocytes from an infant with LAD were unable to ingest 50% of the Pseudomonas aeruginosa strains studied, which indicates a requirement for CR3. However, the remaining strains were phagocytosed in the absence of CR3, and ingestion was blocked by monoclonal antibodies directed at CD14. This CR3/CD14 receptor bias was further confirmed by using thioglycollate-elicited murine peritoneal macrophages, which have nonfunctional CR3 before activation. Results indicate that either CR3 or CD14 is involved independently in nonopsonic phagocytosis of different P. aeruginosa strains. Clearance of P. aeruginosa from the endobronchial space may be facilitated by nonopsonic phagocytosis, since low levels of opsonins are present. The impact of lung infection with P. aeruginosa may be determined, in part, by the phagocytic receptor that mediates ingestion.

Adult↗

PubMed2001

Inducible expression of exogenous genes in Dictyostelium discoideum using the ribonucleotide reductase promoter.

We report here the development of a regulated gene expression system for Dictyostelium discoideum based on the DNA-damage inducibility of the rnrB gene. rnrB, which codes for the small subunit of the enzyme ribonucleotide reductase, responds to DNA-damaging agents at all stages of the D.discoideum life cycle. Doses that have little effect on development have previously been shown to increase the level of the rnrB transcript by up to 15-fold. Here we show that all elements necessary for DNA-damage induction are contained in a 450 bp promoter fragment. We used a fusion of the rnrB promoter with the gene encoding GFP to demonstrate an up to 10-fold induction at the RNA level, which appears in all aspects similar to induction of the endogenous rnrB transcript. Using a fusion with the lacZ gene we observed an up to 7-fold induction at the protein level. These results indicate that the rnrB promoter can be used to regulate the expression of specific genes in D.discoideum. This controllable gene expression system provides the following new characteristics: the induction is rapid, taking place in the order of minutes, and the promoter is responsive at all stages of the D.discoideum life cycle.

4-Nitroquinoline-1-oxide↗

PubMed2001

Biphasic expression of rnrB in Dictyostelium discoideum suggests a direct relationship between cell cycle control and cell differentiation.

Cell differentiation in Dictyostelium is strongly affected by the cell cycle. Cell cycle control is well-understood in other systems, but this has had almost no impact on the study of Dictyostelium cell differentiation, in part because the cell cycle in Dictyostelium is unusual, lacking a G1 phase. Here we describe the cell-cycle regulated expression of rnrB, which codes for the small subunit of ribonucleotide reductase and is a marker of late G1 in many systems. There appear to be two expression peaks, one in mid-G2 and the other near the G2/M transition. Using Xgal/anti-BrdU double staining, we show that cells in asynchronously growing cultures express in both phases, with a gap between them during which the gene is transcriptionally silent. Cold-synchronized cells show exclusively G2/M expression, while mid-G2 expression is seen in high-density synchronized cells and can also be inferred in cells undergoing synchronization by either method. rnrB expression occurs in other systems shortly after cells pass a point (the "restriction point" or "start") at which they commit to complete their current cell cycle. We demonstrate a similar commitment point in Dictyostelium and show that this occurs shortly before the mid-G2 rnrB expression peak. The Dictyostelium cell cycle thus appears to include a well-defined though inconspicuous event, between early and mid-G2, with some features which are normally associated with the G1/S transition. Others have described a switch from stalk to spore differentiation preference at about this time. Since Dictyostelium cells switch back from spore to stalk preference approximately at the G2/M rnrB expression maximum, cell differentiation as well as rnrB expression may be regulated directly by fundamental cell cycle control processes.

Animals↗

PubMed2001

Treatment of vitamin K deficiency in cystic fibrosis: Effectiveness of a daily fat-soluble vitamin combination.

OBJECTIVE: Patients with cystic fibrosis (CF) and pancreatic insufficiency (PI) commonly have vitamin K deficiency, and those with CF-associated liver disease (CFLD) have universal vitamin K deficiency. We evaluated the effectiveness of an oral fat-soluble vitamin combination (ADEKs) to treat patients with vitamin K deficiency. STUDY DESIGN: Patients with PI and CF (mean age, 15 years; range, 0.6 to 46 years) including 6 with advanced CFLD were prospectively enrolled in a study of a fat-soluble vitamin combination taken on a daily basis. None had received vitamin K supplementation for at least 4 months before the study. Fat-soluble vitamin combination supplementation was given for a minimum of 4 months; the mean vitamin K intake was 0.18 mg/d (SD = 0.1, range, 0 to 0.3). The primary outcome was change in plasma PIVKA-II (prothrombin in vitamin K absence). RESULTS: Before supplementation 58 (81%) of 72 patients had abnormal PIVKA-II levels (>2.9 ng/mL). After supplementation 29 (40%) had abnormal PIVKA-II levels (P =.001). All 6 patients with advanced CFLD had abnormal PIVKA-II levels (median, range of 20.8, 5.5 to 55 ng/mL) before treatment, which corrected to normal in 50% (4.1, 2.1 to 65 ng/mL). Four patients, 2 with CFLD, had a prolonged prothrombin time (>13.5 seconds) at both time periods. CONCLUSIONS: An oral fat-soluble vitamin combination with a modest amount of vitamin K can, as a daily supplement, improve the PIVKA-II levels in patients with PI and CF.

Adolescent↗

PubMed2001

Nonopsonic phagocytosis of Pseudomonas aeruginoas: insights from an infant with leukocyte adhesion deficiency.

Children with leukocyte adhesion deficiency type I are at risk for overwhelming infection because their neutrophils lack surface beta 2 integrins (CD18/CD11) that normally interact with endothelial cell adhesion molecules and mediate migration to sites of bacterial invasion. In vitro studies of phagocytic cells from an infant with leukocyte adhesion deficiency type I demonstrated that complement receptor 3 (CD18/CD11b) mediates nonopsonic phagocytosis of some Pseudomonas aeruginosa strains and might play a control role in the control of Pseudomonas infections at sites where there are low levels of opsonins.

CD18 Antigens↗

PubMed2001

The identification and development of specific monoclonal antibodies to squamous cell carcinoma.

We have developed specific monoclonal antibodies to immunogenic glycoproteins expressed selectively on the cell membrane of squamous cell malignancies. These proteins serve to act as tumor markers that characterize this malignancy; there has be no evidence of cross reactivity to normal epithelial cells. Analysis of patterns of expression reveals that those membrane proteins identified by monoclonals AD7 and 5C6 appear early in cellular transformation to malignancy. At such a time, immunohistochemical recognition is seen in the presence of genotypic alterations, yet phenotypic changes may not be apparent. Of additional interest is that these monoclonal antibodies exhibit strong ADCC allowing the tumor proteins to not only serve as a marker of malignancy but as a target for therapeutic destruction.

Animals↗

PubMed2000

Chinese tonal language rehabilitation following cochlear implantation in children.

Cantonese language rehabilitation in 28 prelingually deaf children who underwent cochlear implantation was evaluated. All patients were implanted with multichannel devices and the operations went smoothly. They all had improved scores on audiological assessments and speech perception tests. The speech evaluation tests included the recognition of sounds, vowels, consonants and tone. Sentence recognition and story comprehension were both improved after training for 2 years. Cochlear implantation is a useful measure for the speech rehabilitation of prelingually profound deaf children when hearing aids are of no benefit. The multichannel implant device is of clinical significance in the rehabilitation of those patients using tonal language.

Child↗

PubMed1999

Regulation of the ribonucleotide reductase small subunit gene by DNA-damaging agents in Dictyostelium discoideum.

In Escherichia coli, yeast and mammalian cells, the genes encoding ribonucleotide reductase, an essential enzyme for de novo DNA synthesis, are up-regulated in response to DNA damaging agents. We have examined the response of the rnrB gene, encoding the small subunit of ribonucleotide reductase in Dictyostelium discoideum, to DNA damaging agents. We show here that the accumulation of rnrB transcript is increased in response to methyl methane sulfonate, 4-nitroquinoline-1-oxide and irradiation with UV-light, but not to the ribonucleotide reductase inhibitor hydroxyurea. This response is rapid, transient and independent of protein synthesis. Moreover, cells from different developmental stages are able to respond to the drug in a similar fashion, regardless of the basal level of expression of the rnrB gene. We have defined the cis -acting elements of the rnrB promoter required for the response to methyl methane sulfonate and 4-nitroquinoline-1-oxide by deletion analysis. Our results indicate that there is one element, named box C, that can confer response to both drugs. Two other boxes, box A and box D, specifically conferred response to methyl methane sulfonate and 4-nitroquinoline-1-oxide, respectively.

4-Nitroquinoline-1-oxide↗

PubMed1999

Identification of cis-regulating elements and trans-acting factors regulating the expression of the gene encoding the small subunit of ribonucleotide reductase in Dictyostelium discoideum.

We have examined the promoter of rnrB, the gene encoding the small subunit of ribonucleotide reductase of Dictyostelium discoideum, using lacZ as a reporter gene. Deletion analysis showed that expression of this gene in vegetative cells involves an A/T-rich element, whereas its expression in prespore cells during development requires a region encompassing two G/C-rich elements, designated box A and box B. Removal of boxes A and B results in very low level of activity. When either box A or box B is deleted, prestalk cells adjacent to the prespore zone also express beta-galactosidase. The behavior of these cis-regulatory elements implies that the mechanism regulating the prespore-specific expression of rnrB is different from that regulating other known prespore genes. We have used electrophoretic mobility shift assays to identify factors that interact with box A and box B. Box A interacts with a factor that is found in the nuclear fraction. While box B interacts with a factor that is present in the cytosolic fraction throughout growth and development, its presence in the nuclear fraction is developmentally regulated. Results from competition assays suggest that both box A and box B interact with transcriptional activators that have not been characterized previously.

Animals↗

PubMed1999

Potential for fraudulent use of digital radiography.

BACKGROUND: Digital radiographic images can be manipulated using personal computers. To test the potential for fraudulent use, the authors altered a series of dental radiographs, printed them to simulate duplicated films and submitted them for authorization of proposed treatment. MATERIALS AND METHODS: The authors obtained periapical radiographs of teeth that contained small restorations or were unrestored from the files of three dental patients at a private dental practice. The authors used a flatbed scanner to digitize and import the radiographs into a computer. Then they added dental caries, large restorations, fractures and periapical pathosis to the radiographs. The authors proposed to the insurance companies that the teeth in question be restored using expensive treatment, such as root-canal therapy and full-coverage crowns. RESULTS: In each case, the insurance companies authorized the proposed treatment based on the appearance of the teeth on the radiographs. The altered images illustrated an apparent need for dental treatment that was not required and that could have led to payment for treatment that was not actually performed. CONCLUSIONS: This study illustrates the potential for the fraudulent use of manipulated digital radiographic images. CLINICAL IMPLICATIONS: Dentistry should be aware of the implications of the potential for such abuse and should develop measures both to prevent it from occurring and to facilitate its detection.

Computer Security↗

PubMed1998

Technical hints for high dose rate interstitial tongue brachytherapy.

High dose rate (HDR) interstitial tongue brachytherapy is a new treatment modality. This study describes important technical details required for its successful use. Thirteen patients with carcinoma of the oral tongue were treated solely with interstitial brachytherapy using HDR remote afterloading techniques during the years 1994-1997. The afterloading catheters were positioned by the submandibular approach with the assistance of a template set. Custom-made mandibular lead shields were inserted prior to treatment. Special reusable Tuen Mun Hospital (TMH) lead buttons were made for improved radiation protection. The median dose given was 55 Gy in ten fractions over 6 days. The interfraction interval was 7 hours for the first seven patients treated and was extended to 8 hours for the other six. Shrinking field techniques were employed and the treatment length of the last fraction was reduced by 5 mm. Commencing with the second patient treated with double planar implants, the medial plane was treated with eight fractions while the lateral plane received ten fractions. To reduce further the potential risk of tract seeding, additional coverage to the implantation tracts was given for the last four patients, with the resultant isodose curves resembling a 'comb rake/brush'. The mean and median measured doses on the inner face of the mandibular shields were 113% and 93% of the reference dose respectively (range 77-247). The dose to the corresponding sites on the gingival surface can be reduced by 75% if the 3 mm thick lead shield is placed successfully. With the use of the TMH button, the transmitted dose to the tissue in direct contact can be reduced by one-third. With the 'comb rake/brush' dose distribution, the high dose volume of the single planar implants could be reduced by 44%, compared with the low dose rate technique, if loading to just 5 mm short of the submandibular skin was required. The mean doses for the combination of eight double planar plus two single planar implants, and ten double planar implants, are on average 29% and 37% greater than the reference dose respectively. An 8% reduction in absolute dose in the region between the planes of the catheters would lead to an even greater magnitude of reduction in morbidity to late responding tissue. The prerequisite for the success of HDR interstitial implants is to develop a good technique in positioning the afterloading catheters and protection of the normal tissue. Its importance merits special attention if HDR remote afterloading interstitial tongue brachytherapy is to realize its full potential.

Brachytherapy↗

PubMed1998

Xenotransplantation of adult porcine islets in diabetic mice. A study of UVB irradiation, cryopreservation and immunosuppression on graft survival time.

The major obstacle for successful xenotransplantation of islets to large animals and human diabetics is the host rejection. To address the rejection problem, we studied the efficacy of UV-B irradiation, cryopreservation and immunosuppression on the in vivo functional time and immunogenicity of adult porcine islets (PI) in outbred CD1 mice. Exposure of PI to UV-B irradiation between 300-1800J/M2 did not affect the cellular viability as assessed by fluorescein diacetate or their daily insulin secretion in vitro. Fresh PI normalized the blood glucose (BG) of diabetic CD1 mice for 3.1+/-0.6 (n = 8, mean+/-SEM) days. Islets treated with 600J/M2 UV-B irradiation or cryopreservation had similar graft functional times to fresh islets upon transplantation in diabetic CD1 mice. Immunosuppression with cyclosporin A (CsA), antilymphocyte serum (ALS) and FK506 prolonged the functional time of fresh pig islets to 7.9+/-0.9 (n = 9), 6.2+/-1.3 (n = 5) and 24.2+/-10.4 (n = 12) days, respectively. However, additional pretransplant treatment with either UV-B irradiation or cryopreservation did not further increase the functional time of pig islets in mice immunosuppressed with CsA. Furthermore, there was no apparent difference in the frequency of appearance of cytotoxic antibodies and antibody titers in the recipients of UV-B irradiated or cryopreserved pig islet compared with non-treated islets. The UV-B irradiation and cryopreservation of PI before transplantation with the present protocols did not appear to have significant effect on the islet immunogenicity when assessed by in vivo survival duration and anti-donor antibody titer production.

Animals↗

PubMed1998

Immunotherapy of colon cancer using chimeric mAb 31.1.

We have produced two monoclonal antibodies specific for membranes of colon carcinoma cells that demonstrate minimal if any cross reactivity with normal colon tissue. The antigen of one of the two antibodies (mAb 33.28) is extremely immunogenic eliciting both cell mediated and humoral immunity. The monoclonal antibodies developed in in vitro studies suggested strong antibody dependent cell cytotoxicity (ADCC) for both antibodies, but somewhat stronger for the mAb 31.1. The murine version of mAb 31.1 produced approximately 90% tumor cell destruction in the same period of time. Nude mice with LS174T xenografts (human colon carcinoma) were challenged with 1 x 10(6) cells given subcutaneously in the thigh. By day 10, well animals were incapacitated by tumor growth. Among those animals receiving 400 micrograms of intraperitoneal chimeric 31.1 at day one, all were protected and remained free of disease. Those challenged with chimeric antibody and human effector cells at day 7 demonstrated regression of established tumor nodules among 80% of the animals so treated. Therapy of patients with extensive primary as well as metastatic colon cancer may be found to respond to the above form of therapy post surgery, when employed alone or in combination with an effective cytotoxic (chemotherapeutic) agent.

Animals↗

PubMed1997

A longitudinal study of unsaturated iron-binding capacity and lactoferrin in unstimulated parotid saliva.

Availability of iron is one important nutritional parameter for microbial growth in saliva. This longitudinal study measured the diurnal and day-to-day variations in the total iron (TI), total iron-binding capacity (TIBC), unsaturated iron-binding capacity (UIBC), and lactoferrin (LF) in unstimulated human parotid saliva. Saliva was collected from 15 young male subjects in the morning and afternoon hours each day for five consecutive days. The TI and TIBC were determined by flameless atomic absorption spectroscopy, and UIBC was determined by subtraction of TI from TIBC. The LF was determined by "sandwich" enzyme-linked immunosorbent assay (ELISA). One peripheral blood sample of each subject was also analyzed for TI, TIBC, and ferritin. The results showed no significant diurnal or day-to-day variation of TI, TIBC, UIBC, or LF in saliva for most subjects. However, significant between-subject variations were observed for most parameters. Variations ranged from subjects with constantly positive UIBC values to subjects with constantly negative UIBC values. The relationship between the LF values and the TI and TIBC values suggests that other iron-binding protein(s) are present in saliva. Also, saliva had significantly lower TIBC values than serum. This finding indicated that iron may be easily available in saliva. However, further studies are required to determine the relationship between UIBC value of saliva and oral and dental diseases, and also to detect the presence of other iron-binding proteins in saliva.

Adult↗