Biomedical subjects

Emily Poon

Publications and source records attributed to Emily Poon.

5 recordsLinked to original sources

PubMed2005

Association of testosterone, insulin-like growth factor-I, and C-reactive protein with metabolic syndrome in Chinese middle-aged men with a family history of type 2 diabetes.

CONTEXT: Age-related declines in testosterone and IGF-I are associated with deposition of visceral fat, a component of the metabolic syndrome (MES). OBJECTIVE: Testosterone and IGF-I may interact with familial disposition to diabetes mellitus to increase the association with MES. DESIGN: We conducted a cross-sectional cohort study. SETTING: The study was conducted in a university teaching hospital. SUBJECTS: Study subjects included 179 middle-aged men with a family history of diabetes (FH) (aged 39.1 +/- 8.1 yr) and 128 men without FH (aged 43.8 +/- 8.5 yr). MAIN OUTCOME MEASURES: Clinical characteristics, frequency of MES using the World Health Organization criteria with Asian definitions of obesity (body mass index > or = 25 kg/m2), and serum levels of total testosterone, IGF-I, and high-sensitive C-reactive protein (hs-CRP) were measured. RESULTS: Men with FH had higher frequency of MES than those without FH [39.1 vs. 23.4% (P = 0.004)]. On multivariate analysis, smoking (former and current smokers), low total testosterone, and IGF-I but elevated hs-CRP levels explained 35% of the MES variance in men with FH. The frequency of MES increased with declining tertiles of total testosterone and IGF-I but increasing tertiles of hs-CRP. After adjustment for age and smoking history, subjects with all three risk factors had a 13-fold increase in risk association with MES compared with those without hormonal and inflammatory risk factors. These risk associations were not found in men without FH in whom only smoking (ex and current) and low total testosterone level were independent predictors for MES, which explained 14% of the variance. CONCLUSIONS: Clustering of FH, hormonal abnormalities, and high hs-CRP is associated with MES in Chinese middle-aged men.

Adult↗

PubMed2005

Consistency test of the electron transport algorithm in the GEANT4 Monte Carlo code.

In this work, the condensed history algorithm in GEANT4 (version 4.6.2.p01) is examined. We performed simulations of an ionization chamber composed of water for 1.25 MeV incident photon beams under Fano conditions, and evaluated the consistency of the cavity response for several combinations of electron transport parameters. GEANT4 permits electrons to reach geometric boundaries in large steps, and underestimates lateral displacement near interfaces. Step size artefacts due to distortions in electron fluence and angular distributions reduce the cavity dose by up to 39%. Accurate cavity response can be achieved using severe user-imposed step size restrictions. We suggest that improvements in the electron transport algorithm in GEANT4 should address the handling of boundary crossing.

Algorithms↗

PubMed2005

Accuracy of the photon and electron physics in GEANT4 for radiotherapy applications.

This work involves a validation of the photon and electron transport of the GEANT4 particle simulation toolkit for radiotherapy physics applications. We examine the cross sections and sampling algorithms of the three electromagnetic physics models in version 4.6.1 of the toolkit: Standard, Low-energy, and Penelope. The depth dose distributions in water for incident monoenergetic and clinical beams are compared to the EGSNRC results. In photon beam simulations, all three models agree with EGSNRC to within 2%, except for the buildup region. Larger deviations are found for incident electron beams, and the differences are affected by user-imposed electron step limitations. Particle distributions through thin layers of clinical target materials, and perturbation effects near high-Z and low-Z interfaces are also investigated. The electron step size artifacts observed in our studies indicate potential problems with the condensed history algorithm. A careful selection of physics processes and transport parameters is needed for optimum efficiency and accuracy.

Air↗

PubMed2005

Effect of hepatic lipase -514C->T polymorphism and its interactions with apolipoprotein C3 -482C->T and apolipoprotein E exon 4 polymorphisms on the risk of nephropathy in chinese type 2 diabetic patients.

OBJECTIVE: Triglyceride-rich lipoprotein particles may promote the progression of diabetic nephropathy. Patients with diabetic nephropathy have increased plasma triglycerides and reduced activity of hepatic lipase (HL), which hydrolyzes triglycerides. We hypothesized that the HL -514C-->T polymorphism, which reduces HL expression, and its interactions with polymorphisms in apolipoprotein (apo) E and apoC3 increase the risk of diabetic nephropathy. RESEARCH DESIGN AND METHODS: In a case-control study involving 374 Chinese type 2 diabetic patients with and 392 without diabetic nephropathy, we genotyped the HL -514C-->T, apoE exon 4, and apoC3 -482C-->T polymorphisms. RESULTS: HL -514T-containing genotypes (T+) were associated with diabetic nephropathy (OR = 1.7, P = 0.0009). Adjustment by multiple logistic regression for hypertension, triglycerides, sex, non-HDL cholesterol, BMI, smoking, and alcohol intake did not diminish the association (OR = 1.8, P = 0.003). The association between HL T+ genotypes and diabetic nephropathy appeared stronger in diabetic patients with apoC3 -482 non-TT genotypes (OR = 1.9, P = 0.003) or apoE epsilon2 or epsilon4 alleles (OR = 2.2, P = 0.005). Subjects with HL TT exhibited trends toward increased triglyceride and non-HDL cholesterol levels compared with CC carriers. CONCLUSIONS: HL T+ genotypes might increase the risk of developing diabetic nephropathy by slowing clearance of triglyceride-rich remnant lipoproteins. In concert with other risk factors (e.g., hyperglycemia), lipid abnormalities may damage the kidneys and endothelium, where reduced binding sites for lipases may precipitate a vicious cycle of dyslipidemia, proteinuria, and nephropathy.

Apolipoprotein C-III↗

PubMed2003

Cardiac hypertrophy and remodeling in relation to ACE and angiotensinogen genes genotypes in Chinese dialysis patients.

BACKGROUND: Genetic polymorphisms of the angiotensinogen (AGT) and angiotensin-converting enzyme (ACE) genes are associated with increased risk of hypertension and left ventricular hypertrophy (LVH) in hypertensive subjects. However, the extent to which these polymorphisms are related to LVH and remodeling in dialysis patients remains unknown. METHODS: Two hundred and forty-six end-stage renal disease (ESRD) patients on peritoneal dialysis and 183 control subjects, all of Chinese origin, were genotyped for the ACE insertion/deletion (I/D) and the AGT M235T gene polymorphisms. Left ventricular mass index (LVMi) and relative wall thickness were measured using echocardiography. RESULTS: Prevalence of ACE DD and AGT TT genotype was 14% and 83%, respectively, in ESRD patients and did not differ significantly from controls. A total percentage of 95% of our patients had LVH (171 with concentric and 63 with eccentric hypertrophy). Adjusting for age, gender, body mass index, duration of dialysis, diabetes, renal diagnosis, hematocrit, systolic and diastolic blood pressure, dialysis urea clearance, residual glomerular filtration rate, and use of converting enzyme inhibitors or angiotensin receptor blockers, AGT TT genotype remained independently associated with greater LVMi (coefficient = 28.73; 95% CI, 5.72 to 51.75; P = 0.015) and relative wall thickness (coefficient = 0.072; 95% CI, 0.022 to 0.122; P = 0.005) than MT/MM genotypes. LVMi and relative wall thickness did not differ significantly among patients with DD, DI, and II genotypes. No statistical significant interaction was noted between ACE and AGT gene polymorphism in relation to LVMi and relative wall thickness. CONCLUSION: Polymorphism of the AGT M235T gene but not ACE I/D gene is associated with greater LVMi and relative wall thickness, indicating more concentric LVH, in Chinese peritoneal dialysis patients. Possible synergistic effects between AGT and ACE gene polymorphism require further evaluation in a larger population.

Adult↗