No description available.

No description available.

No description available.

Introduction. Free tissue transfer is the 'gold standard' of surgical care for patients requiring composite tissue reconstruction when local options are unavailable or unsuitable. It is a form of autologous transplant wherein composite tissue is harvested from a distant site and used to reconstruct the primary defect. The flap is rendered ischaemic following transection of its vascular pedicle until successful anastomosis with the recipient vessels is completed. Ischaemia depletes cellular ATP, lowers pH and strains cellular homeostatic mechanisms. The only way to halt the inevitable progression to cell death is by reperfusion. However, reperfusion per se initially worsens the injury through the influx of inflammatory cells and mediators. This biphasic injury is named ischaemia reperfusion injury (IRI) and is characterized by microcirculatory dysfunction primarily mediated by oxidative stress. This can lead to inadequate perfusion and ultimately tissue necrosis. IRI occurs in all transplants, is unavoidable and has no treatment. Preconditioning is an intervention performed before a known event that improves the outcome of that event. The elective nature of transplants permits such interventions to be executed. Haem-­oxygenase 1 (HO-­1) is a cytoprotective enzyme that is up-­regulated in response to diverse stressors including oxidative stress. Haem arginate (HA) is a potent inducer of this enzyme. Pharmacological preconditioning with HA has been shown to reduce IRI and improve clinical outcome in models of visceral IRI. Aim: to investigate whether HA could be used to improve outcome in myocutaneous flaps. Objectives: (1) to establish a reliable model of myocutaneous IRI (2) to assess the effects of pharmacological preconditioning with HA on clinical outcome measures and (3) to investigate the mechanisms underlying the effects of HA preconditioning demonstrated in the in vivo model by in vitro work. Methods. An in situ transverse rectus abdominis myocutaneous (TRAM) flap was developed. Forty male, Lewis rats were randomly assigned to receive IV: Control (NaCl); HA; HA + tin mesoporphyrin (SnMP, an HO-­1 inhibitor) and SnMP alone. Laser Doppler imaging (LDI) scans were performed to assess perfusion. Clinical outcome was assessed by percentage area flap necrosis and perfusion. In vitro adult human epidermal keratinocytes (HEKa) were treated in: Control medium; HA; SnMP and Desferrioxamine (DF) or combinations thereof. MTT and VialightTM plus ATP assays were used to assess cytotoxicity. Intracellular reactive oxygen species (ROS) concentration was determined by flow cytometry (CMH2DCFDA assay). Statistical analysis was performed by one-­way analysis if variance (ANOVA) followed by Tukey's test. Results. In vivo preconditioning with HA increased HO-­1 protein expression and level of bioactivity. This bioactivity was successfully inhibited by SnMP. In the skin, HO-­1 up-­regulation occurred in macrophages. HA based treatments resulted in significantly worse necrosis at 48 h: Control vs HA (p = 0.01). HA based treatments significantly decreased perfusion at: 24 h (Control vs HA, p = 0.0002) and 48 h (Control vs HA, p = 0.04). By contrast, SnMP did not affect either clinical outcome measure. In vitro preconditioning with HA was cytotoxic and increased intracellular ROS: both were reversed by co-­administration of DF but not SnMP. Conclusion. In contrast to data from visceral models, HA preconditioning proved deleterious in myocutaneous flaps. This is most likely due to the generation of ROS by free haem independent of HO-­1 up-­regulation.

Ischaemia-reperfusion (IR) injury is caused by the re-introduction of oxygen to organs, following periods of reduced blood flow (ischaemia). Whilst re-establishing blood flow (reperfusion) to the heart following myocardial infarction is vital for organ survival, this paradoxically leads to tissue damage. Mitochondria are at the heart of IR injury, with succinate dehydrogenase (SDH) a major player in orchestrating the damage. Succinate accumulates during ischaemia and is rapidly oxidised by SDH upon reperfusion, producing reactive oxygen species (ROS), leading to cellular death. I have investigated the development of drugs, aimed at targeting succinate metabolism to ameliorate IR injury. I firstly screened a range of compounds for their ability to inhibit SDH, having been chosen for their similar structures to succinate or the classical SDH inhibitor, malonate. Interestingly, only malonate and oxaloacetate showed potent SDH inhibition, thus were selected for further development. Malonate ester prodrugs with different properties were characterised. Hydrolysis rates of the esters differed greatly, with tuned, labile, malonate esters releasing malonate much more rapidly. Malonate esters were taken up into cells and hydrolysed to release malonate to different extents. Additionally, mitochondria-targetedmalonatemono and diesters were developed, each differing in mitochondrial and cellular uptake andmalonate release. Targeted and nontargeted malonate esters distributed into tissues in vivo, with preliminary in vivo work carried out on IR injury models, to assess for protective effects of the compounds. In addition, the physiological role of the tricarboxylic acid cycle metabolite, itaconate, was investigated. In lipopolysaccharide stimulated macrophages, itaconate has been reported to exert its effects by inhibition of SDH however, I found itaconate was a relatively poor SDH inhibitor, indicating other mechanisms of action. Current prodrugs of itaconate have many non-specific effects, not attributable to itaconate. I therefore characterised a novel itaconate prodrug and found it to be a much better surrogate, which could be subsequently used to elucidate roles for itaconate. Overall, I have shown the importance of ester selection for the prodrug delivery of dicarboxylate molecules and developed methods to improve their biological delivery.

The Slit family of secreted proteins act as axonal repellents during embryogenesis. Slit2 via its receptor, Roundabout-1, also inhibits chemotaxis of multiple leukocyte subsets. Using static and microfluidic shear assays, we found that Slit2 inhibited multiple steps required to recruit circulating neutrophils. Slit2 blocked capture and firm adhesion of human neutrophils to and transmigration across inflamed primary vascular endothelial cells. To determine the response of Slit2 in renal ischemia reperfsuion injury, Slit2 was administered prior to bilateral renal pedicle clamping in mice. This led to significant decreases in both renal tubular necrosis score and neutrophil infiltration. Administration of Slit2 also prevented elevation of plasma creatinine following injury in a dose-dependent manner. Furthermore, administration of Slit2 did not increase hepatic bacterial load in mice infected with L.monocytogenes infection. Collectively, these data demonstrate Slit2 as an exciting therapeutic molecule to combat renal ischemia reperfusion injury without compromising protective host innate immune functions.

The Slit family of secreted proteins act as axonal repellents during embryogenesis. Slit2 via its receptor, Roundabout-1, also inhibits chemotaxis of multiple leukocyte subsets. Using static and microfluidic shear assays, we found that Slit2 inhibited multiple steps required to recruit circulating neutrophils. Slit2 blocked capture and firm adhesion of human neutrophils to and transmigration across inflamed primary vascular endothelial cells. To determine the response of Slit2 in renal ischemia reperfsuion injury, Slit2 was administered prior to bilateral renal pedicle clamping in mice. This led to significant decreases in both renal tubular necrosis score and neutrophil infiltration. Administration of Slit2 also prevented elevation of plasma creatinine following injury in a dose-dependent manner. Furthermore, administration of Slit2 did not increase hepatic bacterial load in mice infected with L.monocytogenes infection. Collectively, these data demonstrate Slit2 as an exciting therapeutic molecule to combat renal ischemia reperfusion injury without compromising protective host innate immune functions.

Thesis (Ph. D.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 172-238) Also available in print.

Artemisinin is herbal drug with a wide range of biological and physiological function. It is currently administered in the treatment against uncomplicated F.Palcifarum infections. It has also been shown to be cytotoxic against a variety of cancer cells. Despite the promise of many anti cancer drugs, drug induced cardiotoxicity has constantly threatened drug applicability especially in patients with co-morbities. Artemisinin has been shown to be cardioprotective, although the intracellular pathways remain to be elucidated. In this study, isolated perfused rat hearts were subjected to 35 minutes of ischaemia and 120 minutes reperfusion or primary cardiac myocytes subjected to 120 minutes hypoxia and 120 minutes reoxygenation where artemisinin (4.3μM) was administered in presence and absence of the PI3K inhibitor (wortmannin) (0.1μM), p70S6K inhibitor (rapamycin) (0.1μM), non selective nitric oxide synthase inhibitor (L-NAME) (100μM) and inducible nitric oxide synthase inhibitor (aminoguanidine) (100μM). At the end of the experiment, hearts underwent infarct size to risk ratio assessment via tri-phenyltetrazolium chloride staining or western blot analysis for p-Akt and p70S6K. Cardiac myocytes were assessed for either MTT analysis, cleaved-caspase 3 or for eNOS/iNOS or p-BAD activity using flow cytometry. In isolated hearts, artemisinin (0.1μM-100μM) showed a significant dose dependent decrease in infarct size (P<0.01-0.001 vs. I/R control). It was also shown to significantly improve cellular viability (66.5±6.3% vs. 29.3±6.1% in H/R, P<0.01) and decrease the levels of cleaved caspase-3 compared to the H/R control group (17.1±2.0% vs. 26.8±2.0% in H/R, P<0.001). Artemisinin was shown to confer protection via the activation of the PI3K-Akt-p70S6k cell survival pathway and presented an upregulation in p-eNOS and iNOS expression. Furthermore, co-administering artemisinin with doxorubicin showed artemisinin reverses I/R or H/R injury as well as doxorubicin-induced injury via the nitric oxide signalling pathway. Additionally, in HL-60 cells, the co-administration doubled artemisinins cytotoxicity while also implicating the nitric oxide pathway. This is the first study to shows that artemisinin ameliorates doxorubicin mediated cardiac injury whilst enhancing its cytotoxicity in HL-60 in a nitric oxide dependent manner. This study concluded that artemisinin was both anti apoptotic and protective against myocardial I/R injury via the PI3K-Akt-BAD/P70S6K and via the nitric oxide cell survival pathway as well as pro-apoptotic against HL-60 in a nitric oxide dependent manner.

Thesis (MScMedSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: It is well-established that transient activation of the β-adrenergic signalling pathway with ligands such as isoproterenol, formoterol and dobutamine, elicits cardioprotection against subsequent long periods of ischaemia. Initially the focus was on the β1- and β2-adrenergic receptors (β1-AR, β2-AR), but recently the β3-AR also emerged as a potential target in the treatment of heart disease. In heart failure, β1- and β2-AR are typically known to be down-regulated while β3-ARs, on the other hand, are up-regulated (Moniotte et al., 2001). Thus, it has become important to examine the significance of the β3-AR and its downstream signalling under similar states of stress. It has been shown that β3-AR stimulation is resistant to short term agonist-promoted desensitization in vitro and in vivo (Liggett et al., 1993) and after being activated, this receptor is able to convey continual intracellular signals (Lafontan et al., 1994). Thus, it could be an ideal target for therapeutic intervention, also in ischaemic heart disease. We hypothesized that selective β3-AR stimulation during ischaemia / reperfusion may be cardioprotective, whereas selective inhibition of this receptor may prove useful in the end stages of sustained ischaemia and early reperfusion. Methods: The isolated working rat heart, subjected to 35 min of regional ischaemia (RI) and 60 min reperfusion was used as model. The β3-AR agonist (BRL37344) (1 μM) or antagonist (SR59230A) (0.1 μM) were applied as follows: (i) before 35 min RI (PT), (ii) during the last 10 min of RI (PerT) and /or (iii) at the onset of reperfusion (PostT) and (iv) administration of BRL37344 during the last 10 min of RI BRL37344 (PerT) was followed by SR59230A during first 10 min of reperfusion SR59230A (Post). The contribution of nitric oxide synthase (NOS) in β3-AR was assessed, using the non-specific NOS inhibitor, L-NAME (50 μM). Endpoints were functional recovery and infarct size. In another set of experiments BRL37344 and SR59230A were applied according to the same protocols, but the left ventricle was dissected from the heart and freeze clamped at 10 min reperfusion for Western blot analysis of extracellular signal-regulated kinase (ERK p44/p42), protein kinase B (PKB/Akt), glycogen synthase kinase-3β (GSK-3β), and endothelial nitric oxide synthase (eNOS). Data were analyzed with one or two-way analysis of variance (ANOVA). Results: Administration of the selective β3-AR agonist (BRL37344) (1μM) before 35 min RI (BRL37344 (PT), significantly reduced infarct size when compared to the non-pretreatment group (NPT) (21.43±2.52 vs 43.17±1.20, p < 0.001). BRL37344 had similar effects on infarct size when applied during the last 10 min of regional ischaemia BRL37344 (PerT) (14.94±2.34, vs NPT, p < 0.001) or at the onset of reperfusion BRL37344 (PostT) (19.06±1.81, vs NPT, p < 0.001). When BRL37344 was applied as a (PerT+PostT) strategy, infarct size was once again significantly reduced (20.55±2.01 vs 43.17±1.20, p <0.001). In contrast, administration of the β3-antagonist SR59230A according to the same protocol did not reduce infarct size and values similar to those of untreated hearts (NPT) were obtained. Surprisingly, when BRL37344 was applied during the last 10 min of regional ischaemia followed by the administration of the β3-AR antagonist (SR59230A) at the onset of reperfusion, [BRL37344 (PerT) & SR59230A (PostT)], infarct size was significantly reduced to 20.78±3.02 (p <0.001 vs NPT and SR59230A (PerT + PostT). Involvement of nitric oxide (NO) was shown since the reduction in infarct size elicited by BRL37344 was totally abolished by, L-NAME, when administered in combination with BRL37344 for 10 minutes prior to RI or at the onset of reperfusion for 10 minutes (% infarct size: 41.48±3.18 and 35.75±3.54, p <0.001 vs BRL37344 (PT) and BRL37344 (PostT), respectively. Western blot results show that PKB/Akt is activated by BRL37344 regardless of the time of administration. The intervention BRL37344 (PerT+PostT), exhibited the most significant phosphorylation of PKB/Akt (fold increase: 14.2±3.71, p<0.01 vs NPT and p<0.05 vs BRL37344 (PostT). In addition, BRL37344 (PT), (PerT), (PostT) and [BRL37344 (PerT) +SR59230A (PostT)] showed significant activation of this kinase (2.92±0.22, 5.54±0.43, 4.73±0.47, and 6.60±0.78, respectively). ERKp44/p42 however, was not significantly activated by any of the treatments. Phosphorylation of eNOS and GSK-3β was significant only in the BRL37344 (PerT+PostT) and [BRL37344 (PerT) + SR59230A (PostT)] groups. The activation of eNOS-S-1177 in the BRL37344 (PerT+PostT) group was (2.82±0.46, p<0.01 and 0.05 vs NPT and BRL37344 (PostT), respectively) and in the [BRL37344 (PerT) + SR59230A (PostT)] group was (2.26±0.48, p<0.05 vs NPT). A very significant increased phosphorylation of GSK-3β was seen in the same two groups (68.8±7.73, p<0.001 vs NPT and 25.5±5.42 vs NPT, p<0.05, respectively). Conclusion: β3-AR has potent cardioprotective effects when administered either before, during and after ischaemia during early reperfusion as indicated by the reduction in infarct size as well as activation of PKB, GSK-3β and eNOS. These beneficial effects can be linked to NO production through activation of eNOS. / AFRIKAANSE OPSOMMING: Dit is bekend dat verbygaande aktivering van die β-adrenerge seinpad, met ligande soos isoproterenol, formoterol en dobutamien, die hart teen daaropvolgende lang periodes van iskemie beskerm. Aanvanklik was die fokus op die β1- en β2-adrenerge reseptore (β1-AR, β2-AR); maar onlangs is ook die β3-AR as 'n potensiële teiken in die behandeling van hartsiektes ge-eien. In hartversaking, is dit bekend dat β1- en β2-AR afreguleer word, terwyl β3-ARs, aan die ander kant, opreguleer word (Moniotte et al., 2001). Dit het dus belangrik geword om die belang van die β3-AR en sy stroomaf seinpad onder soortgelyke strestoestande te ondersoek. Dit is bewys dat β3-AR stimulasie teen korttermyn agonis geïnduseerde desensitisering in vitro en in vivo bestand is (Liggett et al., 1993) en wanneer geaktiveer, is hierdie reseptor in staat om intrasellulêre seine voortdurend oor te dra (Granneman, 1995). Dit kan dus ‘n ideale teiken vir terapeutiese intervensie wees, ook in iskemiese hartsiekte. Ons hipotetiseer dat selektiewe β3-AR stimulasie tydens iskemie / reperfusie kardiobeskermende mag wees, terwyl selektiewe inhibisie van hierdie reseptor effektief kan wees in die eindstadia van volgehoue iskemie en vroeë herperfusie. Metodes: Die geïsoleerde werkende rothart, onderwerp aan 35 min van streeksiskemie (SI) en 60 min herperfusie, is as model gebruik. Die β3-AR agonis (BRL37344) (1μM) of antagonis (SR59230A) (0.1 μM), is as volg toegedien: (i) voor 35 min SI (PT), (ii) gedurende die laaste 10 min van SI (PerT) en / of (iii) tydens die aanvang van herperfusie (PostT) en (iv) gedurende die laaste 10 min van SI is BRL toediening BRL37344 (PerT) gevolg deur SR59230A tydens die eerste 10 min van herperfusie SR59230A (Post). Die rol van stikstofoksiedsintase (NOS) in β3-AR is met behulp van die nie-spesifieke NOS inhibitor, L-NAME (50 μM) ondersoek. Eindpunte was funksionele herstel tydens herperfusie en infarktgrootte. In 'n ander reeks eksperimente is BRL37344 en SR59230A volgens dieselfde protokolle toegedien, maar die linker ventrikel is uit die hart gedissekteer na 10 min herperfusie en gevriesklamp vir Western klad analise van ekstrasellulêre-sein gereguleerde kinase (ERK p44/p42), proteïen kinase B (PKB/Akt), glikogeen sintase kinase-3β (GSK-3β), en endoteel stikstofoksied- sintase (eNOS). Data is met een of twee-rigting variansie analise (ANOVA) ontleed. Resultate: Administrasie van die selektiewe β3-AR agonis (BRL37344) (1μM) voor 35 min SI BRL37344 (PT), het die infarktgrootte beduidend verminder vergeleke met die nie-behandelde groep (NPT) (21.43±2.52 vs 43.17±1.20, p<0.001). BRL37344 het ‘n soortgelyke effek op infarktgrootte wanneer dit gedurende die laaste 10 min van streeksiskemie BRL37344 (PerT) (14.94±2.34, vs NPT, p<0.001) of by die aanvang van herperfusie (BRL37344 (PostT) (19.06±1.81, vs NPT, p<0.001) toegedien word. Wanneer BRL37344 as 'n (PerT+PostT) strategie toegedien is, was infarktgrootte weereens beduidend verlaag (20.55±2.01 vs 43.17±1.20, p<0.001). In teenstelling hiermee, het administrasie van die β3-antagonis SR59230A volgens dieselfde protokol, nie infarktgrootte verminder nie en waardes soortgelyk aan dié van onbehandelde harte (NPT) is verkry. Interessant, wanneer BRL37344 gedurende die laaste 10 min van streeksiskemie toegedien is, gevolg deur die administrasie van die β3-AR antagonis (SR59230A) by die aanvang van herperfusie, [BRL37344(PerT) & SR59230A(PostT)], was infarktgrootte aansienlik verminder tot 20.78±3.02 (p<0.001 vs NPT en SR59230A (PerT+PostT). Die betrokkenheid van stikstofoksied (NO) is waargeneem deurdat die vermindering in infarktgrootte ontlok deur BRL37344, heeltemal deur L-NAME opgehef is, wanneer dit in kombinasie met BRL37344 vir 10 minute voor SI of by die aanvang van herperfusie vir 10 minute toegedien is (% infarktgrootte: 41.48±3.18 en 35.75±3.54, p<0.001 vs BRL37344 (PT) en BRL37344 (PostT) onderskeidelik). Western kladresultate toon dat PKB/Akt deur BRL37344 geaktiveer word ongeag die tyd van die administrasie. Die intervensie BRL37344 (PerT+PostT), toon die mees beduidende fosforilering van PKB/Akt (voudige toename: 14.2±3.71, p<0.01 vs NPT en p<0.05 vs BRL37344 (PostT). Daarbenewens het BRL37344 (PT), (PerT), (PostT) en [BRL37344 (PerT) + SR59230A (PostT)] ook beduidende aktivering van hierdie kinase tot gevolg gehad (2.92±0.22, 5.54±0.43, 4.73±0.47 en 6.60±0.78, onderskeidelik). ERKp44/p42 is egter nie deur enige van die behandelings geaktiveer nie. Fosforilering van eNOS en GSK-3β was net beduidend in die BRL37344 (PerT+PostT) en [BRL37344 (PerT) + SR59230A (PostT)] groepe. Die aktivering van eNOS-S-1177 was beduidend in die BRL37344 (PerT+PostT) en [BRL37344 (PerT) + SR59230A (PostT)] groepe. 'n Baie beduidende toename in fosforilering van GSK-3β is in dieselfde twee groepe (68.8±7.73, p<0.001 en 25.5±5.42, p<0.05 vs NPT onderskeidelik) waargeneem. Gevolgtrekking: β3-AR het kragtige kardiobeskermende effekte wanneer dit, hetsy voor, tydens en na iskemie gedurende vroeë herperfusie toegedien word, soos deur die vermindering in infarktgrootte sowel as die aktivering van PKB, GSK-3β en eNOS aangedui is. Hierdie voordelige effekte kan aan NO produksie deur aktivering van eNOS gekoppel word.