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Biomedical subjects

J Cheung

Publications and source records attributed to J Cheung.

43 records · Page 3Linked to original sources
PubMed1997

Fenofibrate plus simvastatin therapy versus simvastatin plus cholestyramine therapy for familial hypercholesterolaemia.

Combination therapy is routinely used to achieve improved cholesterol reduction in familial hypercholesterolaemia. We compared the standard simvastatin plus bile-acid sequestrant (cholestyramine) therapy with simvastatin plus fenofibrate in 29 patients with severe familial hypercholesterolaemia. The fibrate regimen resulted in an 35.1 +/- 10.7% reduction in total cholesterol, a 40.6 +/- 20.5% in LDL cholesterol, 17.2 +/- 56.5% reduction in triglycerides and a 20.3 +/- 52.0% increase in HDL cholesterol. The cholestyramine regimen produced reductions of 29.3 +/- 13.2% in cholesterol, 37.1 +/- 21.9% in LDL cholesterol, and 12.5 +/- 48.9% in triglycerides, and a 5.0 +/- 25.4% rise in HDL cholesterol. The fibrate regimen was significantly more effective in reducing total cholesterol (p < 0.001) and LDL-cholesterol (p = 0.004), and also reduced triglycerides significantly (p = 0.05), compared to the cholestyramine regimen. There were significant improvements in the LDL:HDL cholesterol ratio (3.62 +/- 1.54 vs. 4.00 +/- 1.36; p = 0.05) and in the apolipoprotein B:A1 ratio (1.13 +/- 0.036 vs. 1.20 +/- 0.34; p = 0.05). Gastrointestinal side-effects occurred in 10 patients on cholestyramine therapy, and four patients on fibrate therapy had myalgia. There were no cases of rhabdomyolysis with either regime. No significant differences in liver biochemistry or creatine kinase were seen with either regimen.

Adolescent↗
PubMed1997

Isolation, sequence, and expression of the gene encoding halocin H4, a bacteriocin from the halophilic archaeon Haloferax mediterranei R4.

The first gene to encode a haloarchaeal bacteriocin (halocin H4) has been cloned and sequenced from Haloferax mediterranei R4. Both the signal sequence in the halocin H4 preprotein and the monocistronic halH4 gene have some unusual features. The physiology of halH4 expression reveals that although halH4 transcripts are present at low basal levels during exponential growth, halocin H4 activity first appears as the culture enters stationary phase. As halocin activity levels increase, so do transcript levels, but then activity levels decrease precipitously while transcript levels remain elevated.

Amino Acid Sequence↗
PubMed1995

Microbial etiology and predisposing factors among patients hospitalized for corneal ulceration.

OBJECTIVE: To report the spectrum of microorganisms causing corneal ulceration in patients treated on an inpatient basis and to characterize the predisposing factors. DESIGN: Case series. SETTING: Large university-affiliated hospital in Toronto. PATIENTS: All inpatients with corneal ulcers managed between February 1991 and February 1993 (n = 95). RESULTS: Coagulase-negative staphylococci (30% of the 60 culture-positive cases), Staphylococcus aureus (23%), Streptococcus pneumoniae (12%), Pseudomonas aeruginosa (12%) and Moraxella (7%) were the predominant isolates. Previous eye surgery (cataract extraction in 30 cases [32%], penetrating keratoplasty in 12 [13%] and both procedures in 9 [9%]) was a common predisposing factor. Eleven cases (12%) were associated with the use of contact lenses, in all cases extended-wear soft contact lenses; six patients wore bandage lenses and five wore contact lenses for cosmetic reasons. Pseudomonas was the predominant isolate among contact lens wearers (four cases). Most of the 95 cases involved older patients (average age 62.5 years) with concomitant eye or systemic disease. Sixteen patients (17%) ultimately required penetrating keratoplasty. CONCLUSIONS: Recognition of the risk factors for corneal ulceration and prompt, intensive therapy are important to decrease the morbidity associated with this potentially blinding disease.

Adult↗
PubMed1993

Developmental differences in cardiac myocyte calcium homeostasis after steady-state potassium depolarization: mechanisms and implications for cardioplegia.

We previously reported developmental differences in the response of cytosolic free calcium ([Cai]) to extracellular potassium ([Kex]) depolarization (cardioplegia) in juvenile (4 weeks post partum) and mature (12 to 18 months post partum) cardiac myocytes (rabbit). Our present study explored the physiologic basis for these observations. Single calcium-tolerant cardiac myocytes were isolated by sequential exposure to proteolytic agents, loaded with a fluorescent probe for calcium (fura-2) and [Cai] measured by standard fluorescence techniques. The response of [Cai] to [Kex] depolarization (30 mmol/L) was determined in the presence of varying levels of extracellular calcium [Caex], verapamil, ouabain, and amiloride. At nominal levels of [Caex] (0 mmol/L), no significant increases in [Cai] from the juvenile (2.1% +/- 3.3%) or mature (8.5% +/- 3.1%) myocytes were seen. At increasing [Caex], there was a progressive increase in the response of [Cai] to [Kex] depolarization in mature animals' cells (191.8% +/- 40.7%) but not in the juveniles' cells (28.0% +/- 11.5%). Exposure to verapamil resulted in an approximate 80% reduction in relative increase in [Cai] in the mature compared with 60% in the juvenile myocytes. Finally, ouabain exposure resulted in a significant increase in the relative change of [Cai] in juvenile cells (30% to 126.4% +/- 39.4%) but not in the adults' cells. This increase in the juvenile myocytes was blocked by amiloride. We conclude that increases in cardiac myocyte [Cai] after [Kex] depolarization occur predominantly through the calcium channel in the mature animal and through sodium-calcium exchange in the juvenile.

Aging↗
PubMed1992

Developmental differences in the response of cytosolic free calcium to potassium depolarization and cardioplegia in cardiac myocytes.

Several biochemical and functional characteristics of immature myocardium suggest a diminished capacity to regulate intracellular Ca2+ during stress. In particular, cellular calcium overload has been postulated as an important pathogenetic mechanism accounting for suboptimal functional recovery following cardioplegia in immature myocardium. Using intracellular Fura-2 fluorescence as Ca2+ indicator, we measured cytosolic free calcium ([Cai]) in single myocytes and cell suspensions derived from both juvenile (4 weeks post-partum) and mature (6-12 months post-partum) New Zealand white rabbits. Resting [Cai] in juvenile heart cells (26 +/- 3 nM) were approximately 50% of that found in adult myocytes (55 +/- 5 nM). In addition, on exposure to increasing concentrations of extracellular potassium ([Kex]), adult but not juvenile myocytes exhibited increases in [Cai]. These two observations underscore developmental differences in intracellular Ca2+ homeostasis. Of particular clinical relevance is the [Cai] response to cardioplegia containing 16 mM [Kex]: neither group demonstrated the expected [Cai] increase in response to potassium depolarization. The lack of [Cai] response to cardioplegia was most likely due to the high levels of Mg2+ (32 mM) contained in cardioplegic solutions. We conclude that cellular calcium overload does not occur following exposure to cardioplegia alone. Accordingly, these findings do not account for recognized developmental differences in functional recovery from "myocardial protection".

Age Factors↗
PubMedDate not supplied

Probing surface structure of sarcin domain on ribosomes of Escherichia coli by complementary oligo DNAs and ribosome-inactivating protein.

The regional structure of the sarcin domain of 23S rRNA of Escherichia coli ribosomes was determined by a combinatory approach of oligo DNA probes and the action of alpha-sarcin. The sarcin domain is protected by a reactive complementary oligo DNA probe against the hydrolytic action of alpha-sarcin. This protective effect is dependent upon the length and the complementary sequence of oligo DNA probes that react to ribosomes. Under UV irradiation and using of the primer extension, nucleotides that contacted by reactive oligo DNA probes were determined. Nucleotides at the 3' side of the domain (positions from G2659 to C2676) were targeted by oligo DNA probes that have their sequences to complement the domain, indicating that the 3' side region was exposed on the surface of ribosomes, whereas nucleotides at the 5' side of stem and extented to two bases at the loop (positions from C2646 to A2654) were not accessible to any oligo DNA probes, implying that the region could be buried in ribosomes. This study also provided evidence that the conformation of the sarcin domain is subjected to alteration if the exposed 3' side of domain is targeted by the reactive DNA probe. The importance of the topological arrangement of the sarcin domain that engages in the translocation event during translation is discussed.

Base Sequence↗