Three Essays on Income Shifting, Governance and Accounting Outcomes: Evidence from U.S. Multinational Corporations

This thesis is comprised of three essays. The first examines the relationship between income-shifting incentives and share repurchases. The second essay examines the association of income shifting and financial restatements. The third essay then investigates non-arm’s-length transactions, the existence of offshore financial centres, existence of a transfer pricing agreement and corporate cash holdings in US multinational corporations (MNCs, hereafter)

Regulation of nutrient uptake by AMP-activated protein kinase

AMP-activated protein kinase (AMPK) is the downstream component of a protein kinase cascade that is a key regulator of energy balance at both the cellular and whole-body level. AMPK acts to stimulate ATP production and reduce ATP consumption when cellular ATP levels fall, thereby normalizing energy balance. Given the central role of AMPK in cellular carbohydrate and lipid metabolism, AMPK activation has been proposed to be a therapeutic target for conditions associated with dysfunctional nutrient metabolism including obesity, type 2 diabetes, hepatic steatosis, cardiovascular diseases and cancer. One way by which increased ATP production can be achieved is by increasing the supply of nutrient substrates. In the 1990s, AMPK activation was demonstrated to stimulate glucose uptake in striated muscle, thereby improving substrate supply for ATP production. Subsequently AMPK activation was postulated to underlie the increase in glucose uptake that occurs during muscle contraction. More recently, however, several lines of evidence have demonstrated that AMPK activation is unlikely to be required for contraction-mediated glucose uptake. Furthermore, despite the importance of AMPK in cellular and whole-body metabolism, far fewer studies have investigated either the role of AMPK in glucose uptake by non-muscle tissues or whether AMPK regulates the uptake of fatty acids. In the present review, we discuss the role of AMPK in nutrient uptake by tissues, focusing on glucose uptake out with muscle and fatty acid uptake

AMP-activated protein kinase complexes containing the β2 regulatory subunit are upregulated during and contribute to adipogenesis

AMP-activated protein kinase (AMPK) is a heterotrimer of α catalytic and β and γ regulatory subunits that acts to regulate cellular and whole-body nutrient metabolism. The key role of AMPK in sensing energy status has led to significant interest in AMPK as a therapeutic target for dysfunctional metabolism in type 2 diabetes, insulin resistance and obesity. Despite the actions of AMPK in liver and skeletal muscle being extensively studied, the role of AMPK in adipose tissue and adipocytes remains less well characterised. Small molecules that selectively influence AMPK heterotrimers containing specific AMPKβ subunit isoforms have been developed, including MT47-100, which selectively inhibits complexes containing AMPKβ2. AMPKβ1 and AMPKβ2 are the principal AMPKβ subunit isoforms in rodent liver and skeletal muscle respectively, yet the contribution of specific AMPKβ isoforms to adipose tissue function, however, remains largely unknown. This study therefore sought to determine the contribution of AMPKβ subunit isoforms to adipocyte biology, focussing on adipogenesis. AMPKβ2 was the principal AMPKβ isoform in 3T3-L1 adipocytes, isolated rodent adipocytes and human subcutaneous adipose tissue, as assessed by the contribution to total cellular AMPK activity. Downregulation of AMPKβ2 with siRNA inhibited lipid accumulation, cellular adiponectin levels and adiponectin secretion during 3T3-L1 adipogenesis, whereas downregulation of AMPKβ1 had no effect. Incubation of 3T3-L1 cells with MT47-100 selectively inhibited AMPK complexes containing AMPKβ2 whilst simultaneously inhibiting cellular lipid accumulation as well as cellular levels and secretion of adiponectin. Taken together, these data indicate that increased expression of AMPKβ2 is an important feature of efficient adipogenesis

Asymmetric dimethylarginine positively modulates calcium-sensing receptor signalling to promote lipid accumulation

Asymmetric dimethylarginine (ADMA) is generated through the irreversible methylation of arginine residues. It is an independent risk factor for cardiovascular disease, currently thought to be due to its ability to act as a competitive inhibitor of the nitric oxide (NO) synthase enzymes. Plasma ADMA concentrations increase with obesity and fall following weight loss; however, it is unknown whether they play an active role in adipose pathology. Here, we demonstrate that ADMA drives lipid accumulation through a newly identified NO-independent pathway via the amino-acid sensitive calcium-sensing receptor (CaSR). ADMA treatment of 3T3-L1 and HepG2 cells upregulates a suite of lipogenic genes with an associated increase in triglyceride content. Pharmacological activation of CaSR mimics ADMA while negative modulation of CaSR inhibits ADMA driven lipid accumulation. Further investigation using CaSR overexpressing HEK293 cells demonstrated that ADMA potentiates CaSR signalling via Gq intracellular Ca2+ mobilisation. This study identifies a signalling mechanism for ADMA as an endogenous ligand of the G protein-coupled receptor CaSR that potentially contributes to the impact of ADMA in cardiometabolic disease

The role of AMPK in the regulation of fatty acid transport in adipocytes

Abstract not currently available

ANALYSIS OF THE OMEGA-3 FATTY ACIDS CONTENT IN COMMERCIAL OMEGA-3 SUPPLEMENTS IN ARAB GULF COUNTRIES

The consumption of omega-3 fatty acids has increased over the past years for multiple reported health benefits. The omega-3 fatty acids of particular interest are eicosatetraenoic acid (C20:5n3; EPA) and docosahexaenoic acid (C22:6n3; DHA). High quality supplements are essential for safe intake. Studies from different countries including the United States and South Africa showed discrepancies between measured versus the claimed content of EPA and/or DHA in omega-3 supplements sold in Arab Gulf Countries. Therefore, the objective of this study was to analyze and compare the EPA and DHA content of omega-3 supplements with the contents claimed on the product label. Thirty-one commercial supplements purchased from stores in 3 different countries (Saudi Arabia, Kuwait, and Bahrain) had their fatty acid composition and content were analyzed using Gas- Chromatograph with a 100-m SP-2560 fused silica capillary column. The range of measured EPA was 5.09 mg to 469.63 mg per capsule and for DHA was 10.47 to 357.26 mg per capsule. The percentage of the stated label amount for EPA and DHA ranged from 6.5 to 138.6% and 10.9 to 126.3%, respectively. Using the U.S. Food and Drug Administration (FDA) labeling requirements where a supplement must contain at least 80% of the stated label amount of each component listed, only 43.8% of the supplements were compliant for EPA and 40.6% were compliant for DHA. Additionally, only 21.9% of the measured EPA and DHA fall within the 10% of the stated label amount. These results demonstrate the wide variability between the stated label amounts of EPA and DHA in omega-3 supplements sold in Arab Gulf Countries and the need for governmental agencies to perform testing to ensure compliance

Angiotensin II Exaggerates SARS-CoV-2 Specific T-Cell Response in Convalescent Individuals following COVID-19

Dysregulation of renin−angiotensin systems during coronavirus disease 2019 (COVID-19) infection worsens the symptoms and contributes to COVID-19 severity and mortality. This study sought to investigate the effect of exogenous angiotensin II (Ang-II) on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T-cells response in recovered COVID-19 patients. Human peripheral blood mononuclear cells (PBMCs) were treated with Ang II and then stimulated with a SARS-CoV-2 peptide pool. T-cell responses were measured using flow cytometry, while enzyme-linked immunosorbent assay (ELISA) and intracellular cytokine staining (ICS) assays determined functional capability and polarization. Additionally, the relative level of protein phosphorylation was measured using a phosphokinase array. Our results showed that Ang II treatment significantly increased the magnitude of SARS-CoV-2-specific T-cell response in stimulated PBMCs with a SARS-CoV-2 peptide pool. Moreover, the phosphorylation levels of numerous proteins implicated in cardiovascular diseases, inflammation, and viral infection showed significant increases in the presence of Ang II. The mitogenic stimulation of PBMCs after Ang II and SARS-CoV-2 peptide pool stimulation showed functional polarization of T-cells toward Th1/Th17 and Th17 phenotypes, respectively. Meanwhile, ELISA showed increased productions of IL-1β and IL-6 in Ang II-stimulated PBMCs without affecting the IL-10 level. To our knowledge, this study is the first to demonstrate that Ang II exaggerates SARS-CoV-2-specific T-cells response. Therefore, during COVID-19 infection, Ang II may aggravate the inflammatory response and change the immune response toward a more inflammatory profile against SARS-CoV-2 infection

A-769662 inhibits adipocyte glucose uptake in an AMPK-independent manner

Activation of AMP-activated protein kinase (AMPK) is considered a valid strategy for the treatment of type 2 diabetes. However, despite the importance of adipose tissue for whole-body energy homeostasis, the effect of AMPK activation in adipocytes has only been studied to a limited extent and mainly with the AMP-mimetic 5-aminoimidazole-4-carboxamide-1-b-d-ribofuranoside (AICAR), which has limited specificity. The aim of this study was to evaluate the effect of the allosteric AMPK activators A‑769662 and 991 on glucose uptake in adipocytes. For this purpose, primary rat or human adipocytes, and cultured 3T3-L1 adipocytes, were treated with either of the allosteric activators, or AICAR, and basal and insulin-stimulated glucose uptake was assessed. Additionally, the effect of AMPK activators on insulin-stimulated phosphorylation of Akt and Akt substrate of 160 kDa was assessed. Furthermore, primary adipocytes from ADaM site binding drug-resistant AMPKb1 S108A knock-in mice were employed to investigate specificity of the drugs for the observed effects. Our results show that insulin-stimulated adipocyte glucose uptake was significantly reduced by A‑769662 but not 991, yet neither activator had any clear effects on basal or insulin-stimulated Akt/AS160 signaling. The use of AMPKb1 S108A mutant-expressing adipocytes revealed that the observed inhibition of glucose uptake by A‑769662 is most likely AMPK-independent, a finding which is supported by the rapid inhibitory effect A-769662 exerts on glucose uptake in 3T3-L1 adipocytes. These data suggest that AMPK activation per se does not inhibit glucose uptake in adipocytes and that the effects of AICAR and A-769662 are AMPK-independent