The effects of R(+)-lipoic acid supplementation on regulation of human skeletal muscle pyruvate dehydrogenase

This thesis investigated whole body glucose disposal and the adaptive changes in skeletal muscle carbohydrate metabolism following 28 d of supplementation with 1000 mg R(+)-lipoic acid in young sedentary males (age, 22.1 ± 0.67 yr, body mass, 78.7 ± 10.3 kg, n=9). In certain individuals, lipoic acid decreased the 180-min area under the glucose concentration and insulin concentration curve during an oral glucose tolerance test (OGTT) (n=4). In the same individuals, lipoic acid supplementation decreased pyruvate dehydrogenase kinase activity (PDK) (0.09 ± 0.024 min"^ vs. 0.137 ± 0.023 min'\ n=4). The fasting levels of the activated form of pyruvate dehydrogenase (PDHa) were decreased following lipoic acid (0.42 ± 0.13 mmol-min'kg'^ vs. 0.82 ± 0.32 mmolrnin'^kg"\ n=4), yet increased to a greater extent during the OGTT (1.21 ± 0.34 mmol-min'kg"' vs. 0.81 ±0.13 mmolmin"'kg'\ n=4) following hpoic acid supplementation. No changes were demonstrated in the remaining subjects (n=5). It was concluded that improved glucose clearance during an OGTT following lipoic acid supplementation is assisted by increased muscle glucose oxidation through increased PDHa activation and decreased PDK activity in certain individuals.

Human skeletal muscle pyruvate dehydrogenase phosphatase activity and expression : the effect of aerobic capacity

Activation of pyruvate dehydrogenase (PDH), which converts pyruvate into acetyl-CoA, is accomplished by a pair of specific phosphatases (PDP 1 & 2). A cross-sectional study investigating the effect of aerobic capacity on PDP activity and expression found that: 1) PDP activity and PDP! protein expression were positively correlated with most aerobic capacity measures in males (n=lS), but not females (n=12); 2) only males showed a positive correlation between PDP activity and PDPl protein expression (r=0.47; p=O.05), indicating that the increase in PDP activity in males is largely explained by increased PDPl protein expression, but that females rely on another level for PDP activity regulation; and 3) PDP} and Ela protein expression increase in unison when expressed relative to the E2 core. These data suggest that with increased aerobic capacity there is an increased capacity for carbohydrate oxidation through PDH, via El a, and an increased ability to activate PDH, via PDP, when exercising maximally.

Investigation of the Expression of Glucose Transporter Proteins in Human Cancer Cells

Cancer cells are known to display increased glucose uptake and consumption. The glucose transporter (GLUT) proteins facilitate glucose uptake, however, their exact role in cancer metabolism remains unclear. The present study examined mRNA and protein expression of GLUT1, GLUT3, GLUT4 and GLUT12 in lung, breast and prostate cancer cells and corresponding noncancerous cells. Additionally, GLUT expression was determined in tumours from mice xenografted with human cancer cells. Differences in the mRNA and protein expression of GLUTs were found between cancerous and corresponding noncancerous cells. These findings demonstrate abundant expression of GLUT1 in cancer and highlight the importance of GLUT3 as it was expressed in several cancer cells and tumours. GLUT expression patterns in vitro were supported by the in vivo findings. The study of GLUT protein expression in cancer is important for understanding cancer metabolism and may lead to identification of biomarkers of cancer progression and development of target therapies.

Synthesis of cytochrome P450 inhibitors of vitamin E metabolism

Please consult the paper edition of this thesis to read. It is available on the 5th Floor of the Library at Call Number: Z 9999 C54 O46 2007

Cellular Mechanisms of Resveratrol's Interaction with Mitochondrial Reactive Oxygen Species Metabolism

Resveratrol, a polyphenol found naturally in red wines, has attracted great interest in both the scientific community and the general public for its reported ability to protect against many of the diseases facing Western society today. While the purported health effects of resveratrol are well characterized, details of the cellular mechanisms that give rise to these observations are unclear. Here, the mitochondrial antioxidant enzyme Mn superoxide dismutase (MnSOD) was identified as a proximal target of resveratrol in vitro and in vivo. MnSOD protein and activity levels increase significantly in cultured cells treated with resveratrol, and in the brain tissue of mice given resveratrol in a high fat diet. Preventing the increase in MnSOD levels eliminates two of resveratrol’s more interesting effects in the context of human health: inhibition of proliferative cell growth and cytoprotection. Thus, the induction of MnSOD is a critical step in the molecular mechanism of resveratrol. Mitochondrial morphology is a malleable property that is capable of impeding cell cycle progression and conferring resistance against stress induced cell death. Using confocal microscopy and a novel ‘cell free’ fusion assay it was determined that concurrent with changes in MnSOD protein levels, resveratrol treatment leads to a more fused mitochondrial reticulum. This observation may be important to resveratrol’s ability to slow proliferative cell growth and confer cytoprotection. Resveratrol's biological activities, including the ability to increase MnSOD levels, are strikingly similar to what is observed with estrogen treatment. Resveratrol fails to increase MnSOD levels, slow proliferative cell growth and confer cytoprotection in the presence of an estrogen receptor antagonist. Resveratrol's effects can be replicated with the specific estrogen receptor beta agonist diarylpropionitrile, and are absent in myoblasts lacking estrogen receptor beta. Four compounds that are structurally similar to resveratrol and seven phytoestrogens predicted to bind to estrogen receptor beta were screened for their effects on MnSOD, proliferative growth rates and stress resistance in cultured mammalian cells. Several of these compounds were able to mimic the effects of resveratrol on MnSOD levels, proliferative cell growth and stress resistance in vitro. Thus, I hypothesize that resveratrol interacts with estrogen receptor beta to induce the upregulation of MnSOD, which in turn affects cell cycle progression and stress resistance. These results have important implications for the understanding of RES’s biological activities and potential applications to human health.