Albumin is a major serum protein and is frequently used as a cell culture supplement. It is crucially involved in the regulation of osmotic pressure and distribution of fluid between different compartments. Alveolar epithelial Na+ transport drives alveolar fluid clearance (AFC), enabling air breathing. Whether or not albumin affects AFC and Na+ transport is yet unknown. We therefore determined the acute and chronic effects of albumin on Na+ transport in fetal distal lung epithelial (FDLE) cells and the involved kinase pathways. Chronic BSA treatment strongly increased epithelial Na+ transport and barrier integrity in Ussing chambers. BSA did not elevate mRNA expression of Na+ transporters in FDLE cells after 24 h. Moreover, acute BSA treatment for 45 min mimicked the chronic effects. The elevated Na+ transport was caused by an increased maximal ENaC activity, while Na,K-ATPase activity remained unchanged. Acute and chronic BSA treatment lowered membrane permeability, confirming the increased barrier integrity observed in Ussing chambers. Western blots demonstrated an increased phosphorylation of AKT and SGK1, and PI3K inhibition abolished the stimulating effect of BSA. BSA therefore enhanced epithelial Na+ transport and barrier integrity by activating the PI3K/AKT/SGK1 pathway

Thesis (MScMedSc (Biomedical Sciences. Medical Physiology))--University of Stellenbosch, 2009. / In the heart, endothelial nitric oxide synthase (eNOS) is regarded as the most important constitutively expressed enzymatic source of nitric oxide (NO), a major cardiac signalling molecule. On the whole, NO is regarded as a cardioprotective molecule. The role of eNOS during ischaemia / hypoxia is controversial; however, it is generally accepted that ischaemia / hypoxia results in increased cardiac NO production. Most studies focus either on the whole heart or isolated cell models. As yet, no study has compared findings with regard to NO metabolism in these two distinct models, in a single study. We hypothesise that observations in a whole heart model with regard to increased NO production and eNOS involvement in ischaemia are the result of events on cellular level and that the increase in NO production observed during hypoxia in cardiomyocytes and endothelial cells is at least in part due to the increase in expression and / or activation of eNOS. Furthermore, we hypothesize that these effects are mediated via the PI3-K / PKB pathway. We aimed to measure and compare NO-production and eNOS expression and activation in the whole heart and isolated cardiac cells and measure PKB expression and activation in the cells under normoxic and ischaemic / hypoxic conditions. We also aimed to determine the effects of PI3-K / PKB pathway inhibition on NO production and eNOS expression and activation in isolated cardiac cells under normoxic and hypoxic conditions. Adult rat hearts were perfused and global ischaemia induced for 15 and 20 min. Tissue homogenates of perfused hearts were used for the measurement of nitrites and determination of expression and activation of eNOS. Expression of eNOS in the heart was also determined by immunohistochemical (IHC) analysis. Cardiomyocytes were isolated from adult rat hearts by collagenase-perfusion, and adult rat cardiac microvascular endothelial cells (CMEC) purchased commercially. In the cells, hypoxia was induced by covering cell pellets with mineral oil for 60 min. Cell viability was determined by trypan blue and propidium iodide (PI) staining and intracellular NO production measured by FACS analysis of the NO-specific probe, DAF-2/DA and by measurement of nitrite levels (Griess reagent). Results show that in ischaemic hearts, nitrite production increased by 12 % after 15 min ischaemia and 7 % after 20 min ischaemia. Total eNOS expression remained unchanged (Western Blot and IHC) and activated eNOS (phospho-eNOS Ser1177) increased by 38 % after 15 min ischaemia and decreased by 43% after 20 min ischaemia. In the cells, both viability techniques verified that the hypoxia-protocol induced significant damage. In isolated cardiomyocytes, NO-production increased 1.2-fold (by DAF-2/DA fluorescence), total eNOS expression increased 2-fold and activated eNOS increased 1.8-fold over control. In CMECs, NO-production increased 1.6-fold (by DAF-2/DA fluorescence), total eNOS increased by 1.8- fold and activated eNOS by 3-fold. With regards to our PI3-K / PKB investigations, results showed an increase of 84 % and 88 % in expression vii and activation of PKB (phospho Ser473) in hypoxic cardiomyocytes, respectively. In hypoxic CMECs, there was no change in PKB expression but there was a 69 % increase in phosphorylated PKB. NO production in wortmannin-treated hypoxic cardiomyocytes decreased by 12 % as compared to untreated hypoxic cells. In treated hypoxic CMECs, NO production decreased by 58 % as compared to untreated hypoxic cells. Treatment with wortmannin did not change the expression of eNOS protein in the cardiomyocytes, however, activated eNOS decreased by 41 % and 23 % under baseline and hypoxic conditions in treated cells respectively. There was a significant increase in NO production after exposure to O2 deficient conditions in all models investigated, a trend similar to what previous studies in literature found. However, the source of this NO is not fully understood although it has been discovered that NOS plays a role. Our data reveals similar trends in 15 min ischaemia in whole hearts and 60 min hypoxia in the cells; however, the trends observed at 20 min ischaemia are in conflict with our cell data (i.e. decrease in activated eNOS). This may be due to the severity of the ischaemic insult in whole hearts and/or the presence of other cell types and paracrine factors in the whole heart. Hypoxia increased the activation of PKB in the isolated cardiac cells. Inhibition of the PI3-K / PKB pathway reduced NO production and hypoxia-induced eNOS activation in cardiomyocytes. In conclusion, we have, for the first time, demonstrated that the increase in NO production during hypoxia is due (at least in part) to an increase in eNOS phosphorylation at Ser1177 and that this is mediated via the PI3-K / PKB pathway.

The development of drugs and therapeutic agents for combating infections and human malignancies continues to be a forefront area in both academic and industrial research. This is driven by the rapid emergence of multi-drug resistant bacterial strains and accumulating mutations in cancer targets that is quickly rendering our current arsenal of drugs ineffective for these therapies. Unless new drugs with novel mechanisms of action are identified and developed at a faster pace, we face a losing battle in managing these diseases. The first part of this work concerns with the natural product Simocyclinone D8 (SD8). Simocyclinone D8 is an angucyclinone antibiotic that inhibits DNA gyrase with a novel mechanism of action that has been termed competitive inhibition. Simocyclinone D8 was found to inhibit the growth of both Gram-(+ve) and Gram-(–ve) organisms and also inhibit a fluoroquinolone resistant mutant of DNA gyrase. Inspired by the structure and novel mechanism of action that SD8 displays, we synthesized analogues based on the co-crystal structure of SD8 with DNA gyrase. These compounds were found to inhibit DNA gyrase, albeit by a different mechanism of action than that of SD8. We also conducted studies towards the total chemical synthesis of SD8 and made three out of the four fragments in SD8 in decent yields. The second part of this work is focused on the development of a substrate-competitive covalent inhibitor for protein kinase B (AKT). AKT is a valid target for cancer research with two compounds currently in late stage clinical trials. Developing substrate- competitive inhibitors for kinases is a novel approach in targeting them, with very few examples in the literature. This mechanism has been postulated to overcome common resistance mutations that cancer targets harbor. A major drawback in this approach is the low binding affinity for peptide substrates by kinases. We circumvented this problem of affinity by utilizing a covalent mode of binding and synthesized a potent non-peptide active-site directed irreversible compound that inhibits AKT. Further studies on this compound are underway and are expected to yield a compound that can be used as a therapeutic agent or as a probe for AKT.

Malignant pleural mesothelioma (MPM) is an aggressive, treatment-resistant tumour. Cisplatin (cis-diamminedichloroplatinum (II)) is the best single-agent chemotherapy for MPM, but platinum-based combination therapies give the best overall response rates. However, cisplatin use is limited by resistance and severe side effects. This thesis has increased the knowledge concerning cisplatin-induced cell death in MPM by describing a novel potential therapeutic target, and three novel phenotypes of cisplatin-resistance in a human MPM cell line (P31) and its cisplatin-resistant sub-line (P31res1.2). The novel potential therapeutic target, and one of the novel phenotypes, was cisplatin-resistant pro-apoptotic BH3-only proteins. In the P31 cells, cisplatin transiently increased pro-apoptotic BH3-only proteins during 6 h of exposure. This response was almost completely abrogated in the P31res1.2 cells. De-regulated caspase activity and activation was the second novel phenotype identified. The P31res1.2 cells had earlier, possibly mitochondria-independent, caspase-3 activation, increased basal caspase-3 activity and increased basal cleavage of caspase-8 and -9. Despite these differences, 6-h equitoxic cisplatin exposures rendered 50-60% of the cells apoptotic in both cell lines. The third novel phenotype was abrogated Na+K+2Cl--cotransporter (NKCC1) activity. Although NKCC1 activity was dispensable for cisplatin-induced apoptosis, balanced potassium transport activity was essential for P31 cell survival. Finally, the survival signalling protein Protein Kinase B (PKB or Akt) isoforms α and γ were constitutively activated in a PI3K-independent manner in P31 cells. In the P31res1.2 cells, PKBα and γ activities were increased, and there was PI3K-dependent activation of PKBβ. However, this increase in PKB isoform activity was not strongly associated to the cisplatin-resistance of the P31res1.2 cells.

Inositol phosphates play a fundamental role in many intracellular processes. Of particular importance is the role of phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3] in the protein kinase B (PKB/Akt) signalling pathway. PtdIns(3,4,5)P3 recruits PKB to the cell membrane through binding interactions with its pleckstrin homology (PH) domain. In several human cancers, this signalling pathway is upregulated, resulting in increased cell growth and proliferation. In order to investigate the therapeutic potential of the PtdIns(3,4,5)P3–PH domain binding interaction, it is necessary to develop inositol phosphate-based probes. This DPhil dissertation highlights the synthesis of a number of derivatives of the PtdIns(3,4,5)P3 head group – inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4]. These derivatives incorporated phosphate isosteres at both the 3- and 5-positions of Ins(1,3,4,5)P4, through the utilisation of novel protection and deprotection strategies. In addition, this dissertation highlights the efficient synthesis of the natural product inositol 1,3-bisphosphate [Ins(1,3)P2] and our work towards the synthesis of inositol pyrophosphate derivatives.

Type 2 diabetes is usually caused by a combination of pancreatic β-cell failure and insulin resistance in target tissues like liver, muscle and fat. Insulin resistance is characterised by an impaired effect of insulin to reduce hepatic glucose production and to promote glucose uptake in peripheral tissues. The focus of this study was to further elucidate cellular mechanisms for insulin resistance that may be of relevance for type 2 diabetes in humans. We used rat and human adipocytes as an established model of insulin’s target cells. Glucocorticoids, e.g. cortisol, can induce insulin resistance in vivo. In the present study, pretreatment of rat adipocytes in vitro for 24 h with the cortisol analogue dexamethasone produced a downregulation of glucose uptake capacity as well as a marked depletion of cellular insulin receptor substrate 1 (IRS-1) and protein kinase B (PKB), two proteins suggested to play a critical role in the intracellular signal transduction pathway of insulin. The amount of phosphorylated PKB in response to acute insulin treatment was decreased in parallel to total PKB content. The basal rate of lipolysis was enhanced, but insulin’s antilipolytic effect was not consistently altered following dexamethasone pretreatment. Alterations in blood glucose as well as insulin levels may be of great importance for cellular as well as whole-body insulin resistance. High glucose (≥15 mM) for 24 h induced a decrease in glucose uptake capacity in rat adipocytes and IRS-1 content was reduced whereas IRS-2 was increased. Long-term pretreatment with a high insulin concentration downregulated insulin binding capacity and when combined with high glucose, it produced a pronounced reduction of cellular IRS-1 and 2 content together with insensitivity to insulin’s effect to activate PKB and a decrease in glucose uptake capacity. A common denominator for a decrease in glucose uptake capacity in our rat adipocyte studies seems to be a decrease in IRS-1 content. Adipocytes from type 2 diabetes patients are insulin-resistant, but in our work the insulin resistance could be reversed by incubation of the cells at a physiological glucose level for 24 h. Insulin resistance in fresh adipocytes from type 2 diabetes patients was associated with in vivo insulin resistance and glycemic level and with adipocyte cell size and waist-hip ratio (WHR). As a potential mechanism for postprandial dyslipidemia in type 2 diabetes, we examined the nutritional regulation of subcutaneous adipose tissue lipoprotein lipase (LPL) activity. It was upregulated by ~40-50 % after a standardised lipid-enriched meal and this was very similar in type 2 diabetes patients and control subjects, suggesting that the postprandial hypertriglyceridemia found in type 2 diabetes is not explained by an altered nutritional regulation of LPL in subcutaneous fat. In conclusion, the present work provides evidence for novel interactions between glucocorticoids and insulin in the regulation of glucose metabolism that may potentially contribute to the development of insulin resistance. High levels of glucose and insulin produce perturbations in the insulin signalling pathway that may be of relevance for human type 2 diabetes. Cellular insulin resistance may be secondary to the diabetic state in vivo, e.g. via glucotoxicity. This is supported by our finding that insulin resistance in adipocytes from type 2 diabetes patients can be reversed after incubation at a physiological glucose level. Key words: adipocyte, insulin resistance, type 2 diabetes, insulin signalling, glucose uptake, insulin, glucose, dexamethasone, insulin receptor substrate, protein kinase B, GLUT4, lipoprotein lipase.

No description available.

Impairment of mucociliary clearance with reduced airway fluid secretion leads to chronically inflamed airways. Cystic fibrosis transmembrane conductance regulator (CFTR) is crucially involved in airway fluid secretion and dexamethasone (dexa) has previously been shown to elevate CFTR activity in airway epithelial cells. However, the pathway by which dexa increases CFTR activity is largely unknown. We aimed to determine whether the increase of CFTR activity by dexa is achieved by non-genomic signaling and hypothesized that the phosphoinositide 3-kinase (PI3K) pathway is involved in CFTR stimulation. Primary rat airway epithelial cells and human bronchial submucosal gland-derived Calu-3 cells were analyzed in Ussing chambers and kinase activation was determined byWestern blots. Results demonstrated a critical involvement of PI3K and protein kinase B (AKT) signaling in the dexa-induced increase of CFTR activity, while serum and glucocorticoid dependent kinase 1 (SGK1) activity was not essential. We further demonstrated a reduced neural precursor cell expressed, developmentally downregulated 4-like (NEDD4L) ubiquitin E3 ligase activity induced by dexa, possibly responsible for the elevated CFTR activity. Finally, increases of CFTR activity by dexa were demonstrated within 30 min accompanied by rapid activation of AKT. In conclusion, dexa induces a rapid stimulation of CFTR activity which depends on PI3K/AKT signaling in airway epithelial cells. Glucocorticoids might thus represent, in addition to their immunomodulatory actions, a therapeutic strategy to rapidly increase airway fluid secretion.

Les maladies cardio-vasculaires (MCV), telles que l’hypertension et l’athérosclérose, s’accompagnent de modifications structurales et fonctionnelles au niveau vasculaire. Un fonctionnement aberrant de la migration, l’hypertrophie et la prolifération des cellules musculaires lisses vasculaires (CMLV) sont des évènements cellulaires à l’origine de ces changements. L’endothéline-1 (ET-1) contribue à la pathogénèse des anomalies vasculaires, notamment via l’activation des protéines MAPK et PI3-K/PKB, des composantes clés impliquées dans les voies prolifératives et de croissance cellulaires. Il a été suggéré que le stress oxydant jouerait un rôle intermédiaire dans les effets pathophysiologiques vasculaires de l’ET-1. En conséquence, une modulation de la signalisation induite par l’ET-1 peut servir comme éventuelle stratégie thérapeutique contre le développement des MCV. Il apparaît de nos jours un regain d’intérêt dans l’utilisation des agents phyto-chimiques pour traiter plusieurs maladies. La curcumine, constituant essentiel de l’épice curcuma, est dotée de plusieurs propriétés biologiques parmi lesquelles des propriétés anti-oxydantes, anti-prolifératrices et cardio-protectrices. Cependant, les mécanismes moléculaires de son effet cardio-protecteur demeurent obscurs. Dans cette optique, l’objectif de cette étude a été d’examiner l’efficacité de la curcumine à inhiber la signalisation induite par l’ET-1 dans les CMLV. La curcumine a inhibé la phosphorylation des protéines IGF-1R, PKB, c-Raf et ERK1/2, induite par l’ET-1 et l’IGF-1. De plus, la curcumine a inhibé l’expression du facteur de transcription Egr-1 induite par l’ET-1 et l’IGF-1, dans les CMLV. Ces résultats suggèrent que la capacité de la curcumine à atténuer ces voies de signalisation serait un mécanisme d’action potentiel de ses effets protecteurs au niveau cardiovasculaire. / Cardiovascular diseases (CVDs), including hypertension and atherosclerosis, are associated with vascular functional and structural changes. Some of the cellular events underlying these processes include aberrant vascular smooth muscle cell (VSMC) proliferation, hypertrophy and migration. Endothelin-1 (ET-1) has been implicated in the pathogenesis of vascular abnormalities through the hyperactivation of key components of growth promoting and proliferative signaling pathways, including MAPKs and PI3-K/PKB. Vascular oxidative stress has also been suggested to play an intermediary role in mediating ET-1-induced pathophysiological effects. Interference with ET-1-induced signaling may therefore serve as a potential therapeutic strategy against the progression of cardiovascular disorders. There is presently a surge of interest in the use of plant-derived phytochemicals for the treatment of various diseases. Curcumin, the main constituent of the spice turmeric, exhibits multiple biological properties, amongst them, antioxidant, anti-proliferative and cardioprotective properties. However, the molecular mechanisms of its cardiovascular protective action remain obscure. Therefore, in the present studies, we investigated the effectiveness of curcumin to inhibit ET-1-induced signaling events in VSMC. Curcumin inhibited ET-1-induced as well as IGF-1-induced phosphorylation of IGF-1R, PKB, c-Raf and ERK1/2, in VSMC. Furthermore, curcumin inhibited the expression of transcription factor early growth response-1 (Egr-1) induced by ET-1 and IGF-1, in VSMC. In summary, these results demonstrate that curcumin is a potent inhibitor of ET-1 and IGF-1-induced mitogenic and proliferative signaling events in VSMC, suggesting that the ability of curcumin to attenuate these effects may contribute as potential mechanism for its cardiovascular protective response.

Les maladies cardio-vasculaires (MCV), telles que l’hypertension et l’athérosclérose, s’accompagnent de modifications structurales et fonctionnelles au niveau vasculaire. Un fonctionnement aberrant de la migration, l’hypertrophie et la prolifération des cellules musculaires lisses vasculaires (CMLV) sont des évènements cellulaires à l’origine de ces changements. L’endothéline-1 (ET-1) contribue à la pathogénèse des anomalies vasculaires, notamment via l’activation des protéines MAPK et PI3-K/PKB, des composantes clés impliquées dans les voies prolifératives et de croissance cellulaires. Il a été suggéré que le stress oxydant jouerait un rôle intermédiaire dans les effets pathophysiologiques vasculaires de l’ET-1. En conséquence, une modulation de la signalisation induite par l’ET-1 peut servir comme éventuelle stratégie thérapeutique contre le développement des MCV. Il apparaît de nos jours un regain d’intérêt dans l’utilisation des agents phyto-chimiques pour traiter plusieurs maladies. La curcumine, constituant essentiel de l’épice curcuma, est dotée de plusieurs propriétés biologiques parmi lesquelles des propriétés anti-oxydantes, anti-prolifératrices et cardio-protectrices. Cependant, les mécanismes moléculaires de son effet cardio-protecteur demeurent obscurs. Dans cette optique, l’objectif de cette étude a été d’examiner l’efficacité de la curcumine à inhiber la signalisation induite par l’ET-1 dans les CMLV. La curcumine a inhibé la phosphorylation des protéines IGF-1R, PKB, c-Raf et ERK1/2, induite par l’ET-1 et l’IGF-1. De plus, la curcumine a inhibé l’expression du facteur de transcription Egr-1 induite par l’ET-1 et l’IGF-1, dans les CMLV. Ces résultats suggèrent que la capacité de la curcumine à atténuer ces voies de signalisation serait un mécanisme d’action potentiel de ses effets protecteurs au niveau cardiovasculaire. / Cardiovascular diseases (CVDs), including hypertension and atherosclerosis, are associated with vascular functional and structural changes. Some of the cellular events underlying these processes include aberrant vascular smooth muscle cell (VSMC) proliferation, hypertrophy and migration. Endothelin-1 (ET-1) has been implicated in the pathogenesis of vascular abnormalities through the hyperactivation of key components of growth promoting and proliferative signaling pathways, including MAPKs and PI3-K/PKB. Vascular oxidative stress has also been suggested to play an intermediary role in mediating ET-1-induced pathophysiological effects. Interference with ET-1-induced signaling may therefore serve as a potential therapeutic strategy against the progression of cardiovascular disorders. There is presently a surge of interest in the use of plant-derived phytochemicals for the treatment of various diseases. Curcumin, the main constituent of the spice turmeric, exhibits multiple biological properties, amongst them, antioxidant, anti-proliferative and cardioprotective properties. However, the molecular mechanisms of its cardiovascular protective action remain obscure. Therefore, in the present studies, we investigated the effectiveness of curcumin to inhibit ET-1-induced signaling events in VSMC. Curcumin inhibited ET-1-induced as well as IGF-1-induced phosphorylation of IGF-1R, PKB, c-Raf and ERK1/2, in VSMC. Furthermore, curcumin inhibited the expression of transcription factor early growth response-1 (Egr-1) induced by ET-1 and IGF-1, in VSMC. In summary, these results demonstrate that curcumin is a potent inhibitor of ET-1 and IGF-1-induced mitogenic and proliferative signaling events in VSMC, suggesting that the ability of curcumin to attenuate these effects may contribute as potential mechanism for its cardiovascular protective response.