Axon degeneration is a selective elimination of axons, which plays a crucial role during development, injury, and maintenance of neuronal connections. The p75 neurotrophin receptor (NTR) is responsible for maintaining the specificity of neuronal connectivity in parts of the adult brain by inducing the degeneration of aberrantly growing axons into myelinated tracts. The objective of this study is to identify and characterize the signaling pathways used by p75NTR to mediate axon degeneration on myelin. Since p75NTR signals via JNK/Bax/caspase pathway to cause apoptosis, I asked whether this pathway might also be involved in axon degeneration. I observed that inhibition of JNK or Bax significantly decreased myelin-induced axonal degeneration, while depolarization of axons with potassium chloride prevented axonal degeneration on myelin. Together, these results suggest that p75NTR-dependent, myelin-mediated axon degeneration occurs via JNK/BAX signaling, and that neural activity is important for the prevention of myelin-induced axonal degeneration.

The role of the retinal pigment epithelial cells on the viability and renewal of photoreceptors has been well demonstrated in the Royal College of Surgeons (RCS) strain of rat. These rats are characterized by an inherited time-dependent degeneration of their photoreceptors. This degeneration is apparently due to the inability of the retinal pigment epithelial cells to adequately ingest fragments of photoreceptor membrane that are shed during the course of photoreceptor membrane renewal. The buildup of photoreceptor material in the interphotoreceptor space ultimately leads to the degeneration of photoreceptors in these animals. With regard to the pigment epithelial cells, neither the mechanism mediating the ingestion process in normal rats nor the nature of the defect of this process in RCS rats is understood.It is the goal of this proposed research to assay for the presence of phospholipase C in retinal pigment epithelial (RPE) cells and to determine possible modulators of the enzyme in an attempt to associate this with the process of phagocytosis. / Department of Biology

The Royal College of Surgeons (RCS) rat is an established animal model used to study human retinal dystrophies. This study investigated whether kidney dysfunction accompanies the eye abnormalities seen in this model. Overnight urine collection procedures were used to measure protein excretion in 2, 12, and 22 month old female pigmented RCS rats and control rats (RDY). Clearance experiments were performed in anesthetized rats to measure glomerular filtration rate (GFR) and renal plasma flow rate (RPF). There was an age-related increase in protein excretion in both RCS and RDY rats, but the protein excretion was significantly higher in the RCS rats at 2 and 22 months of age. Whole kidney GFR and RPF were significantly lower in the 22 month old RCS rats, when compared to age-matched RDY rats. These findings suggest that the RCS rat exhibits both kidney and eye abnormalities. / Department of Physiology and Health Science

Eine retrospektive Studie über das Progressionsrisiko asymptomatischer früher Altersabhängiger Makuladegeneration in die symptomatische Spätphase überzugehen. Anhand von Lipofuszin-Mustern, die per Fundusautofluoreszenzmessung erkannt werden können, lassen sich Risikopatienten identifizieren. Diese Methode könnte zukünftig im klinischen Alltag als nicht-invasive, kostengünstige Screening-Methode zur Anwendung kommen, um Risikopatienten einer intensivierten Therapie unterziehen zu können, bevor sie eine Beeinträchtigung ihrer Sehkraft erfahren.

Age-related macular degeneration (AMD) is the leading cause of Government-registered blindness in the elderly of the Western world and has two forms: wet and dry. No current AMD therapies are curative, and most are provided after retinal damage from the disease has already occurred (to preserve what is left of the retina). We have constructed a multi-factorial Phase II randomized, controlled clinical trial, titled: “Omega-3 docosahexaenoic acid(DHA) and eicosapentaenoic acid (EPA) nutritional supplementation to delay the progression of age-related macular degeneration (AMD): The OMEGAlberta Study”. Each day, participants in the experimental arm of this study will receive 600mg DHA and 1200mg EPA, plus Vitalux AREDS antioxidant formula. Based on the physicochemical properties of DHA, EPA, and Vitalux, our aim is to delay the 5-year incident rate of progression of intermediate dry AMD to wet AMD. Several tests will be performed, not only to quantify the incident rate of progression of AMD, but also to gain insight of the physiological mechanisms behind the supplements being provided. If the supplements are proven to delay AMD progression, this knowledge should be implemented by changes in health services and policy relating to public education and the treatment of AMD.

Subsequent to an hypoxic-ischaemic (HI)-insult a multi-faceted complex cascade of events occurs that ultimately results in cellular and neurological impairments within cortical and sub-cortical central nervous system (CNS) regions. In the present studies a modified �Levine� rat-pup model of HI (left carotid artery ligation + 1 hour global hypoxia on post-natal day (PND) 26) was employed to assess the neuroprotective properties of clomethiazole (CMZ; a γ-aminobutyric acid (GABA)A receptor agonist). In this study, histological and electrophysiological paradigms were used to assess the long-term neuroprotective properties of CMZ (414mg/kg/day via mini-pumps). Key enzymes involved in inflammation, namely nitric oxide synthase (NOS) and arginase, were also examined to assess other potential CMZ mechanisms. Assessments were carried out 3- and 90-days post-HI, with extensive ipsilateral CNS lesions evident at a gross histological level, at both the early and long-term stages, with CMZ significantly decreasing the lesion size at 3- and 90-days (P<0.01; P<0.05). Evoked field potential analyses were used to assess hippocampal CA1 neuronal activity ex vivo. Electrophysiological measurements contralateral to the occlusion revealed impaired neuronal function following HI relative to short- and long-term controls (P<0.001, 3- and 14-days; P<0.01, 90-days), with CMZ providing near complete protection (P<0.001 at 3- and 14-days; P<0.01 at 90-days). Both inducible NOS (iNOS) and arginase activities were significantly increased at 3-days (P<0.01), with arginase activity remaining elevated at 90-days post-HI (P<0.05) ipsilaterally. CMZ suppressed the HI-induced increase in iNOS and arginase activities (P<0.001; P<0.05). These data provide evidence of long-term functional neuroprotection afforded by CMZ in a model of HI-induced neurodegeneration. In addition, under conditions of HI, functional deficits were not restricted to the ipsilateral hemisphere and were due, at least in part, to changes in the activity of NOS and arginase. Underlying mitochondrial dysfunction is eminently present in many neuropathological conditions. The full extent of mitochondrial dysfunction in cortical, hippocampal and cerebellar tissues was assessed following HI. Assessment of mitochondrial FAD-linked respiration at both 1- and 3-days post-HI revealed a significant decrease in activity from ipsilateral cortical and hippocampal regions (P<0.001). In addition, significant changes in respiratory function were also evident in contralateral regions and cerebellum, 3-days post-HI (P<0.05). Assessment of the mitochondrial electron transport chain (complexes I-V) and mitochondrial markers of integrity (citrate synthase) and oxidative stress (aconitase) confirmed ipsilateral mitochondrial impairment following HI. Complexes I, II-III, V and citrate synthase were also impaired, in contralateral regions and cerebellum, 3-days post-HI. CMZ treatment provided significant protection to all mitochondrial aspects of neuronal tissue assessed. This study provides evidence of the full extent of mitochondrial damage following an HI-insult and may contribute, in part, to the impairment seen contralaterally. In addition, protection afforded by CMZ extends to preservation of mitochondrial function and integrity. Cerebral ischaemia-induced angiogenesis has been shown within and around infarcted regions and may contribute to a more favourable neurological outcome. The level of angiogenesis was examined using platelet endothelial cell adhesion molecule-1 (PECAM-1 / CD31). CD31 immunolabelling 7-days post-HI revealed a significant increase in angiogenesis compared with non-intervention controls (P<0.001). Treatment with CMZ decreased the level of angiogenesis compared to HI + saline (P<0.001) back to non-intervention control levels. Conversely, N[omega]-nitro-L-arginine methyl ester (L-NAME) treatment (5mg/kg/day) exacerbated the ischaemic lesion (P<0.001) and resulted in a marked decrease in angiogenesis compared to non-intervention controls (P<0.001). The extent of cerebral infarction in these studies is dependent on the level of NOS activity with CMZ increasing total NOS levels compared to HI + saline, while L-NAME halted the HI-induce increase in total NOS activity (P<0.001). These results show for the first time, that angiogenesis may be used as an assessment of neurodegeneration / neuroprotection in pathologies of cerebral ischaemia and are directly correlated with changes in NOS activity. These studies have therefore shown that following HI, damage also occurs contralateral to the occlusion, and is not restricted to the ipsilateral hemisphere. In addition, the neuroprotective effects of CMZ have been shown to extend out to 90-days post-HI, whereby significant protection to CA1 neuronal activity was seen. These studies also provide in vivo evidence that CMZ may also afford neuroprotection via anti-inflammatory pathways, as evidenced by a decrease in iNOS and arginase activities. Furthermore, these studies have also show evidence that angiogenesis (CD31) can be used as a diagnostic tool to assess neuroprotection / neurodegeneration.

Mitoquinone (MitoQ₁₀ mesylate) is a mitochondria-targeted antioxidant for the treatment of neurodegenerative diseases. As the oral bioavailability of mitoquinone is low in rat, it is necessary to better understand the mechanisms of its absorption in rat and in human. The aims of this thesis were 1) to investigate oral absorption mechanisms of mitoquinone in Caco-2 cell monolayers and in a rat intestinal tissue model; 2) to investigate the correlation between chemical structure and permeability of mitoquinone analogues in Caco-2 cell monolayers; and 3) to explore the hypothesis that active transport and/or drug metabolism contribute to the pharmacokinetics of oral mitoquinone in rat. In Caco-2 studies, transport of mitoquinone was polarized with the apparent permeability (P[app]) from basolateral (BL) to apical (AP) (P[appBL to AP]) being >2.5-fold the P[app] from AP to BL (P[appAP to BL]). The P[appBL to AP] value decreased by 26%, 31% and 61% by P-glycoprotein (P-gp) inhibitors verapamil 100 [mu]M, cyclosporine A (CsA) 10 [mu]M and CsA 30 [mu]M, respectively, whereas the P[appAP to BL] increased 71% by CsA 30 [mu]M. Some of the intracellular mitoquinone was reduced to mitoquinol and subsequently metabolized to glucuronide and sulfate conjugates. Apical effluxes of mitoquinol sulfate and mitoquinol glucuronide conjugates were significantly decreased by cyclosporine A 30 [mu]M and the breast cancer receptor protein (BCRP) inhibitor, reserpine 25 [mu]M, respectively. In the presence of 4% bovine serum albumin on the BL side, the P[appAP to BL] was 4.52 � 0.92 x 10⁶ cm/s. Based on a absorption-disposition model, F[a] value of mitoquinone in human is estimated to be 56%. A bellshaped relationship exists between the Caco-2 permeability of mitoquinone analogues and their lipophilicity. Permeability of mitoquinone analogues initially increases as lipophilicity increase, reaches a maximum, and then decreases due to significant cellular accumulation and active efflux. The physicochemical parameters of mitoquinone and its analogues (such as log P or polar surface area) alone do not predict their permeability across the cell membranes. The bidirectional transport of mitoquinone displays polarity across rat ileal mucosa. The P[app] from s to m (P[app s to m) of mitoquinone decreased and P[app m to s] increased but not significantly by P-gp inhibitor CsA 30 [mu]M. The tissue accumulation of mitoquinone was ~16% of the total amount of mitoquinone added. In addition, several phase I and one phase II metabolites generated by rat ileum tissue were detected. Results from pharmacokinetic studies indicate that mitoquinone was poorly (~24%) but rapidly absorbed and conjugated after oral administration. It was quickly excreted as unchanged drug and as its glucuronides (the major metabolites in rat) into intestine where it was reabsorbed. P-gp inhibition studies in rat indicate that inhibition of P-gp may increase the intestinal absorption of mitoquinone, but cannot change its oral bioavailability due to increased first-pass phase II metabolism and decreased enterohepatic recycling. In conclusion, mitoquinone is poorly absorbed in rat but may be well absorbed in human. The barrier functions of intracellular metabolism and the action of P-gp to oral absorption of mitoquinone in human may be less significant, whereas P-gp play an important role in the absorption and disposition of mitoquinone in rat in vivo. These results, together with those from its analogues, demonstrate that the actual absorption profile of a compound depends on its intrinsic membrane permeability, transporter affinity, metabolizing enzyme affinity and plasma protein binding affinity.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.

Tez (Tıpta Uzmanlık) - Süleyman Demirel Üniversitesi, Tıp Fakültesi, Göz Hastalıkları Anabilim Dalı, 2002. / Kaynakça var.

Thesis (Ph.D)--Biomedical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Levenston, Marc; Committee Member: Garcia, Andres; Committee Member: Koros, William; Committee Member: Sambanis, Athanassios; Committee Member: Temenoff, Johnna; Committee Member: Vidakovic, Brani.