Syntheses and in-vitro evaluation of novel adamantane based γ-secretase inhibitors.

Abnormal processing of amyloid precursor protein (APP) by ß - and γ -secretases to produce excess amyloid-ß-peptide is believed to contribute to the pathophysiological cascade that results in Alzheimer's disease. γ -Secretase inhibition or modulation therefore represents a rational approach to the prevention and/or management of AD. Here, we present the discovery and SAR of a class of novel adamantanyl sulfonamide based γ -secretase inhibitors. Activity evaluation was conducted on cell lines overexpressing APP (wild type and Swedish mutation). Our results suggest size threshold and hydrogen bond formation are necessary for inhibitory activity. There was no correlation between compound activity, Log P, and the electronic effect of substituents on the aromatic ring. These compounds possess desirable drug like properties and results of the study can guide a pharmacophore based design of γ -secretase inhibitors.

Potential impact of metabolic acidosis on the fixed-acid Bohr effect in snapper (Pagrus auratus) following angling stress.

Oxygen equilibrium data were obtained for intact erythrocytes from Pagrus auratus and the pH-dependence of the fixed-acid Bohr and Root effects described. Indicators of aerobic-anaerobic poise were then measured following a period of strenuous exercise induced by angling capture. Haematological indices and plasma metabolites were evaluated with respect to their potential impact on the blood oxygen transport mechanism. An increase in post-capture haemoglobin content, blood lactate, and glucose were observed. The fall in caudal venous pH from 7.53 to 7.41, reflecting the acid-base status of blood draining the working tail musculature, remained within the operational zone of the maximal fixed-acid Bohr effect (Phi(7.4-7.8)=-0.95), but above the critical pH at which the Root effect suppresses oxygen transport capacity. These stress-induced changes reflect a strategy of optimal O(2) unloading to tissues with the Root effect unlikely to be expressed in the swimming vasculature.

Thermal effects on the blood respiratory properties of southern bluefin tuna, Thunnus maccoyii.

Thermal effects on the blood respiratory properties of southern bluefin tuna (Thunnus maccoyii) at 10, 23 and 36 degrees C, and at 0.5 and 1.5% CO(2) were investigated. A reversed temperature effect occurred as the oxygen partial pressure required for 50% haemoglobin saturation (P(50)) at 0.5% CO(2) decreased from 2.9 kPa at 10 degrees C to 1.7 kPa at 23 degrees C (apparent heat of oxygenation, DeltaH degrees , =+27 kJ mol(-1)). However, oxygen binding was essentially independent of temperature at warmer temperatures (P(50)=1.7-2.0 kPa from 23-36 degrees C at 0.5% CO(2); DeltaH degrees =-6.5 kJ mol(-1)). Hill's coefficient (n(H)) ranged from 1.3 to 1.6, and there was a large effect of temperature on the Bohr factor (DeltalogP(50)/DeltapH=-1.6 at 10 degrees C and -0.9 at 36 degrees C). This is the first study of whole blood to demonstrate the thermal dependence of DeltaH degrees itself, whereby the oxygen equilibrium curve is more sensitive to temperature in the lowest thermal range examined. We suggest that the functional basis for these observations lies in the necessity to ensure a sufficient oxygen supply to all tissues, including the heart and liver, without suffering from premature or excessive oxygen unloading around the heat exchanger prior to delivery of oxygen to organs and tissues that lie efferent to the exchanger.

Changes in cardiac output during swimming and aquatic hypoxia in the air-breathing Pacific tarpon.

Pacific tarpon (Megalops cyprinoides) use a modified gas bladder as an air-breathing organ (ABO). We examined changes in cardiac output (V(b)) associated with increases in air-breathing that accompany exercise and aquatic hypoxia. Juvenile (0.49 kg) and adult (1.21 kg) tarpon were allowed to recover in a swim flume at 27 degrees C after being instrumented with a Doppler flow probe around the ventral aorta to monitor V(b) and with a fibre-optic oxygen sensor in the ABO to monitor air-breathing frequency. Under normoxic conditions and in both juveniles and adults, routine air-breathing frequency was 0.03 breaths min(-1) and V(b) was about 15 mL min(-1) kg(-1). Normoxic exercise (swimming at about 1.1 body lengths s(-1)) increased air-breathing frequency by 8-fold in both groups (reaching 0.23 breaths min(-1)) and increased V(b) by 3-fold for juveniles and 2-fold for adults. Hypoxic exposure (2 kPa O2) at rest increased air-breathing frequency 19-fold (to around 0.53 breaths min(-1)) in both groups, and while V(b) again increased 3-fold in resting juvenile fish, V(b) was unchanged in resting adult fish. Exercise in hypoxia increased air-breathing frequency 35-fold (to 0.95 breaths min(-1)) in comparison with resting normoxic fish. While juvenile fish increased V(b) nearly 2-fold with exercise in hypoxia, adult fish maintained the same V(b) irrespective of exercise state and became agitated in comparison. These results imply that air-breathing during exercise and hypoxia can benefit oxygen delivery, but to differing degrees in juvenile and adult tarpon. We discuss this difference in the context of myocardial oxygen supply.

Plasma lactate and glucose flushes following burst swimming in silver trevally (Pseudocaranx dentex: Carangidae) support the "releaser" hypothesis.

Silver trevally (Pseudocaranx dentex) are highly athletic marine teleosts inhabiting the tropical waters of the Great Barrier Reef, Australia. Burst swimming increased plasma lactate from 1.6 +/- 0.4 S.D. to 21.6 +/- 3.3 mM (N = 6), among the highest values reported for functional hypoxia in fish. These data support the hypothesis that elite swimmers release lactate produced in the myotome into the circulation following anaerobic burst activity. The fish further developed a hyperglycaemic response to burst exercise with plasma glucose increasing from 6.6 +/- 2.0 to 13.2 +/- 2.3 mM (N = 6). Post-exercise erythrocyte swelling also occurred, but nucleoside triphosphate levels remained unaltered and do not provide a mechanism to modulate haemoglobin function during exercise. Metabolism of the blood cells appeared to be fuelled by both lactate and glucose.

Red blood cell function and haematology in two tropical freshwater fishes from Australia.

Salmon catfish and tarpon occur in habitats that periodically become deficient in oxygen resulting in high mortalities of other fish species. The water-breathing catfish, Arius leptaspis, and the facultative air-breathing tarpon, Megalops cyprinoides, both have high haemoglobin and haematocrit, and the oxygen carrying capacity in the air-breather is exceptionally high (15.6+/-1.2 vol%). Iso-pH oxygen equilibria of the red blood cells at 25 degrees C revealed high affinity (P(50)=9 mmHg, pH 7.4) and co-operativity (n(50)>2.2, pH 7.4) in the catfish, and contrasted with low affinity (P(50)=32 mmHg, pH 7.4) and co-operativity (n(50) approximately 1) in the air-breathing tarpon. Oxygen binding was further distinguished by relative pH insensitivity (Bohr factor, Ø=Deltalog P(50)/Deltalog pH=-0.22) in the catfish, compared with a significant Bohr effect in the tarpon (Ø=-0.96). The potential for modulation of haemoglobin-oxygen affinity was indicated by a high ratio of GTP to ATP in the erythrocytes of the catfish, whereas regulation in the tarpon appeared due to ATP alone. Differences in blood respiratory functions between the two species are likely to reflect reduced opportunity for activity under extreme hypoxia in the catfish.

Partitioning of respiration between the gills and air-breathing organ in response to aquatic hypoxia and exercise in the pacific tarpon, Megalops cyprinoides.

The evolution of air-breathing organs (ABOs) is associated not only with hypoxic environments but also with activity. This investigation examines the effects of hypoxia and exercise on the partitioning of aquatic and aerial oxygen uptake in the Pacific tarpon. The two-species cosmopolitan genus Megalops is unique among teleosts in using swim bladder ABOs in the pelagic marine environment. Small fish (58-620 g) were swum at two sustainable speeds in a circulating flume respirometer in which dissolved oxygen was controlled. For fish swimming at 0.11 m s(-1) in normoxia (Po2 = 21 kPa), there was practically no air breathing, and gill oxygen uptake was 1.53 mL kg(-0.67) min(-1). Air breathing occurred at 0.5 breaths min(-1) in hypoxia (8 kPa) at this speed, when the gills and ABOs accounted for 0.71 and 0.57 mL kg(-0.67) min(-1), respectively. At 0.22 m s(-1) in normoxia, breathing occurred at 0.1 breaths min(-1), and gill and ABO oxygen uptake were 2.08 and 0.08 mL kg(-0.67) min(-1), respectively. In hypoxia and 0.22 m s(-1), breathing increased to 0.6 breaths min(-1), and gill and ABO oxygen uptake were 1.39 and 1.28 mL kg(-0.67) min(-1), respectively. Aquatic hypoxia was therefore the primary stimulus for air breathing under the limited conditions of this study, but exercise augmented oxygen uptake by the ABOs, particularly in hypoxic water.

Oxygen transport capacity in the air-breathing fish, Megalops cyprinoides: compensations for strenuous exercise.

Tarpon have high resting or routine hematocrits (Hct) (37.6+/-3.4%) and hemoglobin concentrations (120.6+/-7.3 gl(-1)) that increased significantly following bouts of angling-induced exercise (51.9+/-3.7% and 142.8+/-13.5 gl(-1), respectively). Strenuous exercise was accompanied by an approximately tenfold increase in blood lactate and a muscle metabolite profile indicative of a high energy demand teleost. Routine blood values were quickly restored only when this facultative air-breathing fish was given access to atmospheric air. In vitro studies of oxygen transport capacity, a function of carrying capacity and viscosity, revealed that the optimal Hct range corresponded to that observed in fish under routine behaviour. During strenuous exercise however, further increase in viscosity was largely offset by a pronounced reduction in the shear-dependence of blood which conformed closely to an ideal Newtonian fluid. The mechanism for this behaviour of the erythrocytes appears to involve the activation of surface adrenergic receptors because pre-treatment with propranolol abolished the response. High levels of activity in tarpon living in hypoxic habitats are therefore supported by an elevated Hct with adrenergically mediated viscosity reduction, and air-breathing behaviour that enables rapid metabolic recovery.

The effect of strenuous exercise and beta-adrenergic blockade on the visual performance of juvenile rainbow trout, Oncorhynchus mykiss.

It is hypothesised that the visual performance of rainbow trout, Oncorhynchus mykiss, will be impaired by strenuous exercise as a result of metabolic stress (blood lactacidosis) that activates the Root effect and limits the oxygen-carrying capacity of blood flowing to the eye. The ability to resolve high contrast objects on a moving background, as a measure of visual performance, was quantified pre- and post-exercise using the optomotor response. Strenuous exercise induced a metabolic acidosis (8.0 mmol l(-1) blood lactate) and a significant red cell swelling response but no change in the optomotor response threshold (120 min of arc) was observed. Beta-adrenergic blockade (propranolol) abolished post-exercise red cell swelling but optomotor response thresholds were still maintained at 120 min of arc despite a significant blood lactate load (7.8 mmol l(-1)). The choroid rete mirabile of the trout is extremely well developed (rete area:eye area = 0.39) and may maintain visual performance by ensuring a relatively direct supply of oxygen to the central regions of the avascular retina. Exercised fish under beta-adrenergic blockade exhibited an enhanced optomotor response at 240-300 min of arc. Assuming that these responses reflect "tunnel vision", adrenergic regulation of red cell function may preserve a high ocular PO(2) gradient that satisfies the oxygen demand of peripheral retinal cells.

The aerobic physiology of the air-breathing blue gourami, Trichogaster trichopterus, necessitates behavioural regulation of breath-hold limits during hypoxic stress and predatory challenge.

Physiological characteristics of the blood oxygen transport system and muscle metabolism indicate a high dependence on aerobic pathways in the blue gourami, Trichogaster trichopterus. Haemoglobin concentration and haematocrit were modest and the blood oxygen affinity (P50=2.31 kPa at pH 7.4 and 28 degrees C) and its sensitivity to pH (Bohr factor, phi=-0.34) favour oxygen unloading at a relatively high oxygen pressure (PO2). The intracellular buffering capacity (44.0 slykes) and lactate dehydrogenase (LDH) activity (154.3 iu g(-1)) do not support exceptional anaerobic capabilities. Air-breathing frequency in the blue gourami is expected to increase when aquatic oxygen tensions decline. Under threat of predation, however, this behaviour must be modified at a potential cost to aerobic metabolism. We therefore tested the hypothesis that metabolic responses to predatory challenge and aquatic hypoxia are subject to behavioural modulation. Computer-generated visual stimuli consistently reduced air-breathing frequency at 19.95, 6.65 and 3.33 kPa PO2. Bi-directional rates of spontaneous activity were similarly reduced. The metabolic cost of this behaviour was estimated and positively correlated with PO2 but not with visual stimulation thus indicating down-regulation of spontaneous activity rather than breath-holding behaviour. Neither PO2 nor visual stimulation resulted in significant change to muscle lactate and ATP concentrations and confirm that aerobic breath-hold limits were maintained following behavioural modulation of metabolic demands.