published_or_final_version / Medicine / Master / Master of Philosophy

published_or_final_version / Pharmacology and Pharmacy / Doctoral / Doctor of Philosophy

Obesity is a rising global health burden. The accumulation of fat in the body is associated with metabolic syndrome, type 2 diabetes, cardiovascular disease, hypertension and cancer. Currently available anti-obesity medications are not effective and safe to meet the medical need for obesity management. Prostaglandin E receptor subtype 4 (EP4) is involved in the development of adipocytes, but the signaling in adipogenesis and the effect on the regulation of energy homeostasis is not clear to understand. Thus, EP4 receptor and its signaling pathway are interest for research. The purpose of this dissertation is to investigate the morphology and metabolic alteration in mice and to elucidate whether the lack of EP4 by administration of L-161,982, a selective EP4 antagonist, could influence lipid metabolism of the adipocytes in subcutaneous white adipose tissue. Our findings revealed that whether the mice were fed with normal or high-fat diet, EP4 has no significant influence on the adipocyte size in subcutaneous white adipose tissues. The lack of EP4 also showed no significant effect on the basal or stimulated lipolysis of subcutaneous white adipose tissue. However, EP4 deficiency reverses hepatic lipid storage in high-fat fed mice compared to those fed with normal diet. In conclusion, EP4 might be altered lipid metabolism in the liver, which is crucial in the management of obesity. Prospective studies are essential to investigate the effect of EP4 and its signaling pathway on adiposity and lipid metabolism in the liver. / published_or_final_version / Pharmacology and Pharmacy / Master / Master of Medical Sciences

The objective of this investigation was to identify the appropriate isotopic fractionation factor for total body water (TBW) from ²H₂O enrichment in respiratory water vapor (RW) compared to serum (S), then to use the RW technique to estimate absolute TBW volumes and TBW relative to fat-free body mass (FFB) in three age groups (prepubescent, PP, age = 5-10 y; young adult, YA, age = 22-39 y; older adult, OA age = 65-84 y) of healthy white males and females. The effects of analytical technique (infrared spectrophotometry, IR versus isotope-ratio mass spectrometry, IRMS) and ambient relative humidity on estimates of TBW were also investigated. The composition of the FFB was estimated using a multi-component statistical model (body density, TBW and bone mineral density), and the errors associated with the traditional two-component formula for percent fat from body density were calculated. Our results demonstrated a significant (p < 0.0001) ²H₂O fractionation effect of 0.971 ± 0.005 (mean ± SEM, n = 36) for TBW from RW compared to S. Analysis by IR and IRMS were highly correlated (R² =.999) but IR values were significantly (p < 0.001) higher than IRMS. Deuterium enrichment in RW samples collected at ambient RH (∼20%) was significantly higher (Δ = 20.2 ± 4.5 ppm, mean ± SEM, p < 0.0005) than in RW samples collected at 100% RH, roughly equivalent to a 1.2 L (3.2%) difference in TBW. Total body water relative to FFB mass (W/FFB) was lower (p < 0.01) in YA males (71.0 ± 1.0%) and females (70.2 ± 1.3%) than in PP (boys = 73.1 ± 1.6%; girls = 72.2 ± 1.4%, mean ± SD). In OA, W/FFB was higher (p < 0.05) than in YA (OAM = 72.6 ± 1.1%; OAF = 72.2 ± 1.4%). The density of the FFB was 1.0996 and 1.0839 g/ml in OAM and OAF, respectively. Percent fat from density plus TBW and BMD was lower than from density alone in all groups but YA males, where it was 2.4 percent fat higher. In PP, the Siri density formula resulted in an overestimate of 5.8 ± 2.6 percent fat (mean ± SD, range = 1.4 to 13.6%). In OA females, the density formula overestimated percent fat by 4.4 ± 2.8% (range = 0 to 10.4%). In conclusion, RW corrected for isotopic fractionation will provide acceptable estimates of TBW, although the effects of analytical technique and RH should be controlled. The existence of age-related differences in FFB composition causes errors when the two-component model is used to estimate percent fat in PP and OA females.

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White adipose tissue (WAT) is now recognised as an endocrine organ through its secretion of hormones and protein factors - ‘adipokines’.  This thesis examined the regulation of two adipose expressed genes, retinol binding agent (RBP) involved in retinol transport, and tissue factor (TF) which initiates the extrinsic coagulation cascade.  RNA was isolated and RBP and mRNA levels determined by chemiluminescence-based Northern blotting.  TF and mRNA levels were determined by real-time PCR.  WAT RBP mRNA levels were second only to liver, and TF mRNA levels were highest in WAT depots.  RBP and TF mRNA were detected predominantly from mature adipocytes.  Obesity was not associated with altered RBP and TF gene expression except of for a significant (<i>p</i><0.05) decrease in RBP mRNA from subcutaneous WAT of obese rodent models.  Primary adipocytes were treated with <span lang=EN-GB style='font-family:Symbol'>b-agonists, dexamethasone or leptin.  Only dexamethasone significantly (<i>p</i><0.05) reduced RBP mRNA levels.  TF mRNA levels were unaltered following <span lang=EN-GB style='font-family:Symbol'>b-agonists, forskolin, or dexamethasone treatment except for a significant (<i>p</i><0.05) increase with a high dose of BRL 37344 (a <span lang=EN-GB style='font-family:Symbol'>b₃ agonist).  Administration of two isoforms of retinoic acid significantly decreased RBP gene expression, with 9-<i>cis</i> showing more potency (<i>p</i><span lang=EN-GB style='font-family:Symbol'>£ 0.001) that all-<i>trans</i> (<i>p</i><0.05.  The thiazolidinediones ciglitazone and rosiglitazone were administered, high doses significantly reducing RBP gene expression (<i>p</i> <span lang=EN-GB style='font-family:Symbol'>£ 0.001 and <i>p </i><span lang=EN-GB style='font-family:Symbol'>£ 0.05 respectively).  Fasting and cold exposure are two physiological stimuli which stimulate substrate flux and the release of fatty acids from WAT.  RBP gene expression in WAT was unaltered with fasting, cold exposure and <span lang=EN-GB style='font-family:Symbol'>b-agonist injection.  These studies suggest WAT may be an important source of RBP and TF.  In contrast to lipolysis and leptin production, the SNS does not significantly regulate RBP and TF gene expression.  The high TF gene expression in rodent WAT suggests an association between TF and the cardiovascular disease seen with obesity.

Background: Physical activity (PA) reduces visceral adipose tissue (VAT) in adults; however, the dose to reduce VAT in youth is unclear. Objective: To examine whether high intensity PA preferentially reduces waist circumference (WC) and VAT compared to lower intensity PA. Design: Randomized controlled trial. Participants: Youth were 13-18yrs, overweight, with one additional risk factor for type 2 diabetes (T2DM). Intervention: 6-months, exercising 3 times/week at a high intensity (70-85% of Heart Rate Reserve HRR), or low intensity (40-55% HRR). Primary outcome: VAT (cm2) measured by MRI at L4-L5, and WC at the height of the iliac crest (cm). Results: 94 Youth were randomized to either high intensity (n=30); low intensity (n=32) or control (n=32). Changes in WC and VAT were not significant across groups. A trend towards a reduction in VAT in the training groups, compared to controls was demonstrated in sub-analysis (-14.3 ± 9.6 % vs. +0.01 ± 0.4 %, p= 0.059). Peak fitness increased significantly in both the high and low intensity arms (1.3 ± 0.6 and 1.4 ± 0.6 ml/kg/min, p < 0.05). Conclusions: Training at 55-65% HRR improves fitness by ~10%, and ~2 days/week elicits modest non-significant reductions in VAT in overweight youth.