Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Background: Perinatal ischemic brain injury leads to developmental disability (DD), which accounts for 30% of disabilities in children. Antepartum risk, or risk occurring prior to birth occurs in more than 90% of cases. This study investigated whether maternal ingestion of a natural health product (broccoli sprouts) would provide neuroprotection in an intrauterine model of HI. Methods: Intrauterine ischemia was induced by bilateral uterine artery ligation (BUAL) on E20 of gestation. Rats were fed broccoli sprouts (200 mg) from E15 until postnatal day 14 (PD14). Rat pups underwent neurobehavioural testing from birth to PD21 and were then sacrificed for neuropathologic assessment on PD21. Results: BUAL ligation resulted in growth restriction (IUGR) of the fetuses, which persisted throughout the study (p < 0.001). Reflex testing indicated IUGR pups were developmentally delayed compared to controls (p < 0.001). Open field testing on PD21 indicated hyperactivity in IUGR animals compared to controls (p < 0.001). Histological assessment showed a reduction in pyramidal cells in CA1 and CA3 of IUGR hippocampi and in myelin basic protein (MBP) immunohistochemistry signal. Broccoli sprout supplementation improved some reflex and behavioural measures, increased cell counts in CA1 and CA3 as well as MBP signal in growth restricted animals. Conclusions: Supplementation with broccoli sprouts during the last trimester of gestation and the first 2 weeks of life in the rat lessened the effects of chronic intra-uterine ischemia. These findings suggest a novel approach to the prevention of DD associated with perinatal HI.

Leukocyte adhesion to cerebral endothelial cells plays a critical role in the inflammatory response following transient global cerebral ischemia but its contribution to delayed neuronal cell death is not completely understood. We compared ischemic mice treated with a monoclonal antibody to β2-integrin adhesion receptors (anti-CD18) or a non-binding control antibody following ischemia. Inflammation was characterized by increased CD18 expression on leukocytes and inflammatory mediators in the peripheral blood and brain tissue. Notably, interleukin-1β, which has been shown to mediate cell death in neurons, was elevated in the blood and brain. Anti-CD18 blocked leukocyte adhesion as well as the inflammatory responses, including interleukin-1β expression in neurons. Blocking leukocyte adhesion protected the structural integrity of the hippocampus, cerebral cortex and thalamus, and preserved spatial. Leukocytes adhesion to endothelial cells plays an important role in the evolution of neurological deficit in global cerebral ischemia despite the lack of transmigration of leukocytes across blood-brain-barrier.

Statins can act as preconditioning agents against ischemia reperfusion (IR)-injury through a mechanism involving cyclooxygenase (COX)-2 and the upregulation of prostaglandin synthesis. The following study investigated the effect of selective and non-selective COX inhibition on rosuvastatin-mediated protection against IR-induced endothelial dysfunction in the human forearm vasculature. Healthy volunteers were randomized to drugs with different COX-inhibiting properties: 81mg aspirin (OD), 325mg aspirin (OD), 400mg ibuprofen (QID), 200mg celecoxib (BID) or placebo. A single dose of 40mg rosuvastatin was also administered 24-hours prior to IR. Endothelial function before and after IR was assessed by measuring flow-mediated dilation of the radial artery. Our results show that 81mg and 325mg aspirin (more COX-1 selective), 400mg ibuprofen (similar selectivity for COX-1/2) and 200mg celecoxib (COX-2 selective) all effectively abolished statin-mediated protection against IR-induced endothelial dysfunction in the forearm (2-way ANOVA, p<0.05). These findings indicate that even partial COX-2 inhibition is sufficient to attenuate statin-induced preconditioning.

Remote ischemic preconditioning (rIPC) through transient limb ischemia induces potent cardioprotection against ischemia reperfusion (IR) injury. I examined the delayed phase of protection that appears 24 hours after the initial rIPC stimulus. The primary objective of this study was to establish a mode of sedation and control treatment for delayed rIPC experiments. I used an ex-vivo, Langendorff isolated-mouse heart preparation of IR injury to examine the delayed effects of an intra-peritoneal (IP) injection, sodium-pentobarbital (SP), halothane and nitrous oxide (N2O) anesthesia on post-ischemic cardiac function. Each anesthetic method improved left-ventricular function after IR injury. SP and halothane anesthesia also reduced LV infarct size. Delayed cardioprotection after IP injections was associated with an increase in phosphorylated-Akt levels. The present study shows that IP injections and inhalational anesthesia invoke cardioprotection and, therefore, indicates that these modes of sedation should not be used as control treatments for studies examining the delayed rIPC phenotype.

Statins can act as preconditioning agents against ischemia reperfusion (IR)-injury through a mechanism involving cyclooxygenase (COX)-2 and the upregulation of prostaglandin synthesis. The following study investigated the effect of selective and non-selective COX inhibition on rosuvastatin-mediated protection against IR-induced endothelial dysfunction in the human forearm vasculature. Healthy volunteers were randomized to drugs with different COX-inhibiting properties: 81mg aspirin (OD), 325mg aspirin (OD), 400mg ibuprofen (QID), 200mg celecoxib (BID) or placebo. A single dose of 40mg rosuvastatin was also administered 24-hours prior to IR. Endothelial function before and after IR was assessed by measuring flow-mediated dilation of the radial artery. Our results show that 81mg and 325mg aspirin (more COX-1 selective), 400mg ibuprofen (similar selectivity for COX-1/2) and 200mg celecoxib (COX-2 selective) all effectively abolished statin-mediated protection against IR-induced endothelial dysfunction in the forearm (2-way ANOVA, p<0.05). These findings indicate that even partial COX-2 inhibition is sufficient to attenuate statin-induced preconditioning.

Remote ischemic preconditioning (rIPC) through transient limb ischemia induces potent cardioprotection against ischemia reperfusion (IR) injury. I examined the delayed phase of protection that appears 24 hours after the initial rIPC stimulus. The primary objective of this study was to establish a mode of sedation and control treatment for delayed rIPC experiments. I used an ex-vivo, Langendorff isolated-mouse heart preparation of IR injury to examine the delayed effects of an intra-peritoneal (IP) injection, sodium-pentobarbital (SP), halothane and nitrous oxide (N2O) anesthesia on post-ischemic cardiac function. Each anesthetic method improved left-ventricular function after IR injury. SP and halothane anesthesia also reduced LV infarct size. Delayed cardioprotection after IP injections was associated with an increase in phosphorylated-Akt levels. The present study shows that IP injections and inhalational anesthesia invoke cardioprotection and, therefore, indicates that these modes of sedation should not be used as control treatments for studies examining the delayed rIPC phenotype.

Since caloric restriction (CR) can modify multiple pathways central to the ischemic cascade and enhance neuroplasticity mechanisms, we hypothesized that CR should exert protective effects following brain ischemia. Previous studies have suggested benefit when CR was administered prior to ischemia. This study investigated whether prolonged CR beginning after global ischemia would result in lasting protection as assessed by performance in the open field, as a measure of functional outcome, and hippocampal CA1 neuronal counts. Adult male Mongolian gerbils were subjected to five minute bilateral carotid artery occlusion (I) or sham surgery (S) with tympanic temperature maintained at 36.5 ± 0.2ºC during the intra-ischemic period. After screening out gerbils with incomplete ischemia, each of the two surgical groups were randomly assigned to control diet (CON) or 30% CR for the duration of the study (60d). Gerbils were tested in the open field on d3, 7, 10, 30 and 60. Ischemic animals on control diet showed a significantly higher level of activity in the open field (impaired habituation) compared to SCON gerbils on all test days (p<0.001). Open field activity was decreased 9% in the ICR group versus ICON gerbils on d7 (p=0.024), suggesting a transient neuroprotective effect. Open field activity of the SCR gerbils began increasing relative to that of SCON gerbils during the last 30 days of the study (p=0.055 on d60), raising the question of suitability of the open field test for long-term studies of CR and ischemia. Brain sections obtained at d60 were stained with hematoxylin & eosin. Hippocampal CA1 neuron counts were reduced 88% by ischemia (p<0.001), and there was no sparing effect of CR. These findings suggest that prolonged CR administered beginning after global ischemia cannot diminish brain injury or enhance long-term recovery.

Die Entwicklung mesenterialer Ischämien nach Herzoperationen beruht auf einem Zusammenspiel vieler Faktoren und kann trotz ständiger Verbesserung des prä- intra- und postoperativen Managements nicht generell vermieden werden. Durch eine frühzeitige Diagnostik und Therapie ist es jedoch möglich, die Prognose der mesenterialen ischämischen Ereignisse nach Herzoperationen zu verbessern. In dieser retrospektiven Fall- Kontroll- Studie, welche auf prospektiv erfassten Patientendaten beruht, wurden sowohl anamnestische als auch intra- und postoperative Faktoren hinsichtlich ihres Einflusses auf die Entstehung von mesenterialen Ischämien untersucht. Zielsetzung dieser Arbeit war es, das Patientengut mit erhöhtem Risiko für die Entwicklung einer mesenterialen Ischämie darzustellen, um so Risikopatienten frühzeitig zu identifizieren, und sie einer erweiterten Diagnostik und Therapie zuführen zu können. Im Ergebnis konnten wir das Vorhandensein arterieller Verschlusskrankheiten sowie präoperatives Vorhofflimmern als Risikofaktoren identifizieren. Als Ausdruck einer Kreislaufinstabilität zeigten die Ischämiefälle deutlich häufiger Zeichen eines kardialen Schocks und waren auf eine Kreislaufunterstützung angewiesen. Diese Kreislaufinstabilität setzt sich auch intra- und postoperativen fort und findet sich in einem postoperativen Low Cardiac Output wieder. Zusätzlich gefährdet waren auch Patienten mit postoperativen Retentionsstörungen, cerebrovaskulärer Ereignissen sowie dem Auftreten von Gerinnungsstörungen. Alle diese Patienten sollten nach herzchirurgischen Eingriffen daher besonders intensiv hinsichtlich des Auftretens mesenterialer Ischämien beobachtet werden, um unter Einbeziehung der klinischen Symptome, Laborparameter und bestehenden Risikofaktoren eine zeitnahe Diagnostik zu ermöglichen. Hierdurch ist es möglich, die Letalität durch eine schnelle und gezielte Therapie zu senken.