Lipoprotein(a) (Lp(a)) has been identified as an emerging risk factor for the development of vascular diseases. The Lp(a) particle is assembled in a 2-step process upon secretion of the LDL and apo(a) components from hepatocytes. Work done by the Koschinsky group has identified an oxidase-like activity present in the conditioned medium (CM) harvested from human hepatoma (HepG2), as well as HEK 293 (human endothelian kidney) cells that catalyzes the rate of covalent Lp(a) formation. We have taken a candidate enzyme approach to identifying this oxidase activity. Specifically, we have proposed that the QSOX (Quiescin/sulfhydryl oxidase) is responsible for catalysis of covalent Lp(a) assembly. An oxidase activity assay developed by Dr. Thorpe (University of Delaware) was used to detect QSOX1 in CM harvested from cultured cell lines that catalyze covalent Lp(a) assembly. In addition, the QSOX1 transcript was identified in each cell line and quantified with the use of Real-Time RT-PCR. Quantitative assays of covalent Lp(a) assembly were performed to study some characteristics of the unkwown oxidase activity. First, conditioned medium was dialyzed through a 5 kDa cutoff, as this has previously been shown to reduce the aforementioned oxidase activity. Purified QSOX was then added back to the reaction and the rate of catalysis was observed. The addition of QSOX appeared to enhance the rate of covalent Lp(a) assembly in a dose-dependent manner. Additional covalent Lp(a) assembly assays were performed where various chemicals were added to determine whether Lp(a) assembly was affected. The addition of EDTA did not affect covalent assembly, suggesting that the oxidase activity may not be metallo-dependent. Moreover, dose-dependent addition of Calcium, DTT, Copper and glutathione to dialyzed medium also did not affect the rate of Lp(a) assembly. Taken together, these studies will aid in identifying the nature of the oxidase activity that catalyzes covalent Lp(a) assembly. This will provide us with valuable information on how Lp(a) particles are assembled, and may lead to the development of drugs inhibiting Lp(a) formation. / Thesis (Master, Biochemistry) -- Queen's University, 2008-09-29 12:13:24.786

Diss. (sammanfattning) Umeå : Univ., 2005. / Härtill 4 uppsatser.

It is known that endurance-trained athletes possess higher levels of high density lipoprotein cholesterol (HDL-C) than sedentary controls, and it has been shown in previous studies that acute exercise may elevate these levels even further. The purpose of this study was to investigate the acute exercise response of the plasma HDL's and to determine if the magnitude of the acute response would be affected by the intensity of the exercise. Twelve men (19-41 yrs) ran an equivalent distance (9-12 km) on a treadmill on two separate occasions. On one occasion the exercise was performed at a speed corresponding to 60% of the subject's VO₂ max, and on the other occasion at a speed corresponding to 90% of VO₂ max. Changes in total cholesterol (TC), triglycerides (TG), HDL-C, HDL Apoprotein A (HDL-A), HDL Saturation (HDL-C/HDL-A), lactate (LA) and free fatty acids ( FFA) were measured, and all values were corrected for changes in plasma volume. There were significant increases (p<.01) in HDL-C, HDL-A, and HDL saturation with exercise at both intensities, but greater increases in HDL-C (25% vs 14%) and HDL-A (18% vs 8%) were observed with the higher intensity exercise. Plasma FFA and TG were no different between conditions, although LA concentration rose significantly during the high intensity exercise. The results indicate that increases in HDL components can occur with a relatively moderate exercise session, and that these increases are directly related to the intensity of the exercise. / Thesis / Master of Science (MSc)

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