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K Hoang

Publications and source records attributed to K Hoang.

11 recordsLinked to original sources
PubMed1999

Subtle overlapping deletions in the terminal region of chromosome 6q24.2-q26: three cases studied using FISH.

Interstitial deletions in the terminal region of chromosome 6 are rare. We describe three new cases with subtle interstitial deletions in the q24-q26 region of the long arm of chromosome 6. The karyotypes were analyzed at a 550 band level. Patient1 is a 9-month-old boy with an interstitial deletion, del(6)(q24.2q25.1), developmental delay, low birth weight, hypotonia, heart murmur, respiratory distress, craniofacial and genital anomalies. This is the first report of a case with deletion del(6)(q24.2q25.1). Patient 2 is a 17-year-old young man with an interstitial deletion del(6)(q25.1q25.3), developmental delay, short stature, mental retardation, autism, head, face, chest, hand and feet anomalies and a history of seizures. For the first time autism was described as a manifestation in 6q deletions. Patient 3 is baby boy with a de novo interstitial deletion, del(6)(q25.1q26), anomalies of the brain, genital organs, limbs and feet. This is the first report of a case with deletion, del(6)(q25.1q26). In all three patients, fluorescence in situ hybridization (FISH) using chromosome 6 painting probe ruled out an insertion. The ESR (6q25.1) and TBP (6q27) probes were used to confirm the breakpoints. Since TBP signal is present in all cases, it confirmed an interstitial deletion proximal to this probe. Patient 1 has a deletion of the ESR locus; Patient 2 and 3 have signals for the ESR locus on both chromosomes 6. Therefore the deletion in Patients 2 and 3 are between ESR and TBP loci distal to that of Patient 1. FISH validated the deletion breakpoints assessed by conventional cytogenetics.

Abnormalities, Multiple↗
PubMed1999

Activation of membrane-associated procaspase-3 is regulated by Bcl-2.

The mechanism by which membrane-bound Bcl-2 inhibits the activation of cytoplasmic procaspases is unknown. Here we characterize an intracellular, membrane-associated form of procaspase-3 whose activation is controlled by Bcl-2. Heavy membranes isolated from control cells contained a spontaneously activatable caspase-3 zymogen. In contrast, in Bcl-2 overexpressing cells, although the caspase-3 zymogen was still associated with heavy membranes, its spontaneous activation was blocked. However, Bcl-2 expression had little effect on the levels of cytoplasmic caspase activity in unstimulated cells. Furthermore, the membrane-associated caspase-3 differed from cytosolic caspase-3 in its responsiveness to activation by exogenous cytochrome c. Our results demonstrate that intracellular membranes can generate active caspase-3 by a Bcl-2-inhibitable mechanism, and that control of caspase activation in membranes is distinct from that observed in the cytoplasm. These data suggest that Bcl-2 may control cytoplasmic events in part by blocking the activation of membrane-associated procaspases.

Apoptosis↗
PubMed1999

Constrictive pericarditis due to coccidiomycosis.

Coccidiomycosis is a fungal infection that rarely causes cardiac disease. Constrictive pericarditis in the setting of disseminated coccidiomycosis can be fatal, despite antifungal therapy and pericardiectomy. We report on a patient with constrictive pericarditis due to localized infection by Coccidioides immitis. The patient underwent successful surgical pericardiectomy and antifungal chemotherapy, and remains well 1 year later.

Adult↗
PubMed1999

Static three-dimensional modelling of prolonged seated posture.

Prolonged seating can cause musculo-skeletal problems in the long term if poor postures are adopted. A three dimensional static model of the body to calculate the intervertebral disc compression at the fifth lumbar disc was built. SAMMIE, a computer aided ergonomics package was used for modelling a computer operator workstation and determination of joint centre locations and joint angles in a seated posture. Experimentation was also performed to determine the body-mass distribution on the seat used. No significant difference between male and female body-mass distribution was found. The static model found postures with the seat pan and backrest reclined to predict the lowest disc compression. Postures in which the operator was bent forwards gave the highest disc loadings.

Biomechanical Phenomena↗
PubMed1998

Diabetes and dyslipidemia. A new model for transplant coronary artery disease.

BACKGROUND: Clinical observations suggest that transplant coronary artery disease (TxCAD) is immunologically mediated but may be accelerated by metabolic derangements. We developed a rat model of heterotopic heart transplantation in the presence of diabetes and dyslipidemia to further study their role in TxCAD development. METHODS AND RESULTS: Major histocompatibility complex-mismatched strains of inbred rats underwent heterotopic heart transplantation (ACI-to-Lewis allografts). Diabetes (DM) was induced by streptozotocin injection (80 mg/kg) after transplantation; dyslipidemia was worsened by feeding of a 60% high-fructose diet (+F). Allograft transplants were divided into four groups: (1) +DM/+F; (2) +DM/-F; (3) -DM/+F; and (4) -DM/-F. Isograft transplants (Lewis to Lewis, +DM/+/-F) were controls. All animals received daily cyclosporine (5 mg/kg). Grafts surviving > 30 days were evaluated for TxCAD on histological sections and graded 0 to 5 for intimal thickness. All streptozotocin-treated animals were diabetic within 2 weeks, with fourfold increases in plasma glucose concentrations versus nondiabetics. Severe TxCAD was observed in diabetic allografts only. The mean grade of TxCAD in diabetic allografts was 3.2 +/- 0.5 versus 1.1 +/- 0.4 in diabetic isografts (P < 0.03) and zero TxCAD in nondiabetic allografts (P < or = 0.0001). Fructose feeding resulted in a 1.5-fold higher triglyceride and a 1.3-fold higher cholesterol level versus the regular diet (-F) but showed no independent contribution to the development of TxCAD. CONCLUSIONS: These findings suggest that metabolic derangements associated with diabetes play an important role in TxCAD development in heterotopic ACI-to-Lewis rat heart transplantation. In this model of TxCAD in major histocompatibility complex-mismatched, diabetic, and dyslipidemic rats, immunologic and metabolic mechanisms that contribute to TxCAD can be further delineated and approaches to its prevention assessed.

Animals↗
PubMed1997

Importance of decreased heart rate in predicting transplant coronary artery disease.

Studies in animals and humans have demonstrated that an increased heart rate is a predictor for the development of coronary atherosclerosis and overall cardiovascular mortality. In contrast, we have previously reported that the need for pacemaker implantation because of bradycardia in heart transplant recipients is associated with an increased prevalence of transplant coronary artery disease (TxCAD). Hence, the relevance of changes in heart rate to the development of TxCAD remains unclear. Intra-coronary ultrasound examinations (ICUS) were therefore analyzed in 130 heart transplant recipients (age 50 +/- 11 yr) studied at annual evaluations (3.7 +/- 3.0 yr after transplantation). Quantitative ultrasound measurements were obtained by calculating mean coronary artery intimal thickness (MIT) obtained by examination of the left anterior descending artery. The presence of TxCAD was defined as MIT > 0.3 mm. Resting heart rates (HR) were recorded with the patients in the supine position during routine echocardiography. Based on HR recordings, two groups were defined: group 1, HR below; or group 2, HR above the median. TxCAD was detected in 40% of the ICUS studies overall. The prevalence of TxCAD was higher in group 1 (49%) compared with group 2 (33%), p < 0.05. There was no significant difference in donor ischemic time or donor gender, recipient age, gender, body weight, CMV status, creatinine, total cholesterol, use of lipid lowering drugs or diltiazem. Donor age and use of beta-blockers were higher in group 1 compared with group 2 (29 +/- 10 vs. 25 +/- 9 yr, and 15% vs. 5%, for donor age and beta-blocker use, respectively). By multivariate regression analysis only donor age and years after transplantation were independently correlated with TxCAD. After excluding patients taking beta-blockers and diltiazem, the prevalence of CAD was still higher in group 1 (50%) vs. group 2 (34%). In conclusion, transplant coronary artery disease is more prevalent in patients with lower, rather than higher, heart rates. The reason for this is unclear, but may reflect impaired blood flow to the sinoatrial node.

Adult↗
PubMed1996

Fas-induced activation of the cell death-related protease CPP32 Is inhibited by Bcl-2 and by ICE family protease inhibitors.

The human proto-oncogene bcl-2 and its Caenorhabditis elegans homologue ced-9 inhibit programmed cell death. In contrast, members of the human interleukin-1beta converting enzyme (ICE) family of cysteine proteases and their C. elegans homologue CED-3 promote the death program. Genetic experiments in C. elegans have shown that ced-9 is formally a negative regulator of ced-3 function, but neither those studies nor others have determined whether CED-9 or Bcl-2 proteins act biochemically upstream or downstream of CED-3/ICE proteases. CPP32, like all known members of the CED-3/ICE family, is synthesized as a proenzyme that is subsequently processed into an active protease with specificity for cleavage at Asp-X peptide bonds. In this report, we demonstrate that the CPP32 proenzyme is proteolytically processed and activated in Jurkat cells induced to die by Fas ligation. CPP32 activation is blocked by cell-permeable inhibitors of aspartate-directed, cysteine proteases, suggesting that pro-CPP32 is cleaved by active CPP32 or by other ICE family members. Heterologous expression of Bcl-2 in Jurkat cells prevents Fas-induced cell death as well as proteolytic processing and activation of CPP32. Thus, Bcl-2 acts at or upstream of the CPP32 activation step to inhibit apoptosis induced by Fas stimulation.

Amino Acid Sequence↗
PubMed1995

Physiologically based pharmacokinetic models: mathematical fundamentals and simulation implementations.

This review paper gives an overview of the building blocks of physiologically based pharmacokinetic (PBPK) models and their implementation using computer facilities. The approach focuses on the development of a PBPK model with the most important and appropriate limiting steps for the conditions and exposure scenarios under study. In this approach, the assumptions made in constructing the set of equations, as well as the fitting of variables to specific experimental results, need to be accounted for when making extrapolation to other conditions. A well-constructed PBPK model should account for all possible ranges of extrapolation from the development stages so that appropriate experimental studies and assumptions can be designed to handle the intended applications. Two common assumptions are revisited: the flow-limited assumption and the metabolic clearance using Michaelis-Menten kinetics assumption. Computer hardware and software requirements for implementing PBPK models are briefly reviewed.

Computer Simulation↗
PubMed1987

Evidence for direct inhibition of de novo purine synthesis in human MCF-7 breast cells as a principal mode of metabolic inhibition by methotrexate.

We have investigated the role of dihydrofolate (H2PteGlu) accumulation in the inhibition of de novo purine synthesis by methotrexate (MTX) in human MCF-7 breast cancer cells. Previous studies have shown that cytotoxic concentrations of MTX that inhibit dihydrofolate reductase produce only minimal depletion of the reduced folate cofactor, 10-formyltetrahydrofolate, required for purine synthesis. At the same time, de novo purine synthesis is totally inhibited. In these studies, we show that 10 microM MTX causes inhibition of purine synthesis at the step of phosphoribosylaminoimidazolecarboxamide (AICAR) transformylase, as reflected in a 2-3-fold expansion of the intracellular AICAR pool. The inhibition of purine synthesis coincides with the rapid intracellular accumulation of H2PteGlu, a known inhibitor of AICAR transformylase. When the generation of H2PteGlu is blocked by pretreatment with 50 microM 5-fluorodeoxyuridine (FdUrd), an inhibitor of thymidylate synthase, MTX no longer causes inhibition of purine synthesis. Intermediate levels of H2PteGlu produced in the presence of lower (0.1-10 microM) concentrations of FdUrd led to proportional inhibition of purine biosynthesis, and the exogenous addition of H2PteGlu to breast cells in culture re-established the block in purine synthesis in the presence of FdUrd and MTX. The early phases of inhibition of purine biosynthesis could be ascribed only to H2PteGlu accumulation. MTX polyglutamates, also known to inhibit AICAR transformylase, were present in breast cells only after 6 h of incubation with the parent compounds and were not formed in cells preincubated with FdUrd. The lipid-soluble antifolate trimetrexate, which does not form polyglutamates, produced modest 10-formyltetrahydrofolate depletion, but caused marked H2PteGlu accumulation and a parallel inhibition of purine biosynthesis. This evidence leads to the conclusion that MTX and the lipid-soluble analog trimetrexate cause inhibition of purine biosynthesis through the accumulation of H2PteGlu behind the blocked dihydrofolate reductase reaction.

Acyltransferases↗
PubMed1981

[Use of Doppler ultrasonic examination for per-operative checking of non surgical upper dorsal sympathectomy in the treatment of hyperhydrosis (author's transl)].

Doppler ultrasonic examination has been used as an indirect means of per-operative checking of sweat secretion after non surgical upper dorsal sympathectomy performed by percutaneous injection of hot saline into the upper dorsal sympathetic ganglions for the treatment of palmar hyperhydrosis. Their experience with pre, per and post-operative utilisation of Doppler effect in sixty cases has evidenced a full parallelism between the arterial vasodilation and the decrease in sweat secretion following the destruction of the sympathetic ganglions by hot saline. In the last series of thirty-five cases per-operative use of Doppler ultrasonic examination has spared them failures of the procedure. They consider Doppler ultrasonic examination as a precious help in classical open sympathectomy as well in their non surgical method.

Hand↗