Ellen Koehler-stec - Academia.edu (original) (raw)

Papers by Ellen Koehler-stec

Investigative Ophthalmology & Visual Science, May 1, 2006

Purpose VEGF Trap is a potent antiangiogenic agent that binds and blocks the action of all VEGF-A... more Purpose VEGF Trap is a potent antiangiogenic agent that binds and blocks the action of all VEGF-A isoforms and placental growth factor and, is active in numerous animal models of age-related ocular neovascularization and diabetic retinopathy, when administered either intravitreally or systemically. Moreover, systemic administration of VEGF Trap was active in reducing excess retinal thickness in a Phase I study in age-related macular edema. To understand the pharmacokinetics following intravitreal administration, VEGF Trap (500 mcg) was administered to both eyes of pigmented rabbits. Methods Plasma and eyes were harvested from three animals/time point at defined times to 4 weeks after administration. Concentrations of VEGF Trap, free and bound to VEGF, were determined in plasma, vitreous, choroid, and retina by ELISA. Results Maximal vitreal concentrations of free VEGF Trap were approximately 500 mcg/mL at 0.25 to 6 hours after injection. The drug was cleared from the vitreous in a first order process with a half-life of approximately 4.5 days. Vitreal VEGF:VEGF Trap complex reached a plarteau of 0.6 mcg/mL 10 days after administration. Drug was detected in both retina and choroid, and the elimination profile from these tissues approximated by that of the vitreous. Peak plasma total drug concentrations of 1.6 mcg/mL occurred at 10 days. At 4 weeks, the vitreal free VEGF Trap remained over 10-fold in excess of bound VEGF Trap and the complex levels were on a plateau. Conclusion Given the vitreal half-life, free should remain in excess of bound for at least 3 additional half-lives (13.5 days), suggesting that eye VEGF production would be completely blocked for more than 6 weeks after adminstration of of 500 mcg/eye of VEGF Trap. Commercial interest

Investigative Ophthalmology & Visual Science, May 1, 2003

Biochemical Journal, Dec 1, 1997

Brain Research Bulletin, Mar 1, 1998

Intracerebroventricular (I.C.V.) administration of an inhibitor of nitric oxide synthase (NOS) in... more Intracerebroventricular (I.C.V.) administration of an inhibitor of nitric oxide synthase (NOS) increases oxytocin but not vasopressin secretion, in dehydrated rats [38]. Surprisingly, central injection of L-arginine, the substrate for NOS, caused a similar effect. Kyotorphin (L-tyrosyl-L-arginine), a dipeptide formed from L-arginine by kyotorphin synthetase in the brain may mediate this magnocellular response. Therefore, the dose and time responses of hormone release were compared following I.C.V. injection of kyotorphin and L-arginine to conscious rats that were normally hydrated or deprived of water for 24 h. In water-sated rats, both L-arginine and kyotorphin increased blood pressure and plasma glucose levels coincident with elevating circulating levels of oxytocin, but not vasopressin. In dehydrated animals, both L-arginine and kyotorphin increased plasma oxytocin levels with a similar time course but only kyotorphin decreased vasopressin release. D-arginine, like L-arginine, stimulated secretion of oxytocin, indicating a nonstereospecific effect. A kyotorphin receptor antagonist (L-leucyl-L-arginine) given I.C.V. to dehydrated animals elevated plasma oxytocin and prevented the decrease in vasopressin levels after kyotorphin. Thus, kyotorphin, but not L-arginine, appears to attenuate release of vasopressin either directly from magnocellular neurons or indirectly via modulating compensatory reflexes activated by the pressor response. On the other hand, an excess of L-arginine and kyotorphin within the CNS may mimic the stress response by augmenting release of oxytocin and activating the sympathetic nervous system to increase blood pressure and plasma glucose levels.

Investigative Ophthalmology & Visual Science, May 14, 2008

Clinical Lipidology, Dec 1, 2012

Glucose is the principle energy source for mammalian brain. Delivery of glucose from the blood to... more Glucose is the principle energy source for mammalian brain. Delivery of glucose from the blood to the brain requires its transport across the endothelial cells of the blood-brain barrier and across the plasma membranes of neurons and glia, which is mediated by the facilitative glucose transporter proteins. The two primary glucose transporter isoforms which function in cerebral glucose metabolism are GLUT1 and GLUT3. GLUT1 is the primary transporter in the blood-brain barrier, choroid plexus, ependyma, and glia; GLUT3 is the neuronal glucose transporter. The levels of expression of both transporters are regulated in concert with metabolic demand and regional rates of cerebral glucose utilization. We present several experimental paradigms in which alterations in energetic demand and/or substrate supply affect glucose transporter expression. These include normal cerebral development in the rat, Alzheimer’s disease, neuronal differentiation in vitro, and dehydration in the rat. OOOOOOOO...

Investigative Ophthalmology & Visual Science, 2008

L'invention concerne des compositions et des procedes pour traiter l'obesite ou un etat p... more L'invention concerne des compositions et des procedes pour traiter l'obesite ou un etat pathologique associe a l'obesite, notamment la reduction du poids corporel, l'amelioration des parametres diabetiques, le syndrome du metabolisme, la steatose hepatique, et/ou l'hypertension, a l'aide de l'association de CNTF ou d'une molecule de CNTF et d'un second agent qui est une molecule therapeutique utilisee dans le traitement de l'obesite, du diabete de type II ou tout autre etat pathologique associe a l'obesite.

Investigative Ophthalmology & Visual Science, 2003

L'invention porte sur des compositions et sur des procedes d'administration par voie nasa... more L'invention porte sur des compositions et sur des procedes d'administration par voie nasale ou respiratoire de proteines du facteur neurotrophique ciliaire, notamment dans le traitement de l'obesite et des diabetes gestationnels ou non-insulino dependants.

The AAPS Journal, 2021

There is an urgent demand to develop new technologies to characterize immunogenicity to biotherap... more There is an urgent demand to develop new technologies to characterize immunogenicity to biotherapeutics. Here, we developed an immunocapture LC-MS assay to isotype and semi-quantify monkey anti-drug antibodies (ADAs) to fully human monoclonal antibody (mAb) drugs. ADAs were isolated from serum samples using an immunocapture step with the Fab of the full-length mAb cross-linked to magnetic beads to minimize matrix interference. A positive monoclonal antibody control against the human immunoglobulin kappa light chain was used as a calibration standard for ADA quantitation. The final LC-MS method contains 17 multiple reaction monitoring (MRM) transitions and an optimized 15-min LC method. The results suggested that IgG1 was the most abundant isotype in ADA-positive samples. IgG2 and IgG4 were identified at lower levels, whereas IgG3 and IgA levels were only observed at very minor levels. In addition, levels of total ADA measured by the LC-MS assay were comparable to results obtained us...

American Journal of Physiology-Endocrinology and Metabolism, 1998

Although glucose is the major metabolic fuel needed for normal brain function, monocarboxylic aci... more Although glucose is the major metabolic fuel needed for normal brain function, monocarboxylic acids, i.e., lactate, pyruvate, and ketone bodies, can also be utilized by the brain as alternative energy substrates. In most mammalian cells, these substrates are transported either into or out of the cell by a family of monocarboxylate transporters (MCTs), first cloned and sequenced in the hamster. We have recently cloned two MCT isoforms (MCT1 and MCT2) from a mouse kidney cDNA library. Northern blot analysis revealed that MCT1 mRNA is ubiquitous and can be detected in most tissues at a relatively constant level. MCT2 expression is more limited, with high levels of expression confined to testes, kidney, stomach, and liver and lower levels in lung, brain, and epididymal fat. Both MCT1 mRNA and MCT2 mRNA are detected in mouse brain using antisense riboprobes and in situ hybridization. MCT1 mRNA is found throughout the cortex, with higher levels of hybridization in hippocampus and cerebell...

Biochemical Journal, 1997

Platelets derive most of their energy from anaerobic glycolysis; during activation this requireme... more Platelets derive most of their energy from anaerobic glycolysis; during activation this requirement rises approx. 3-fold. To accommodate the high glucose flux, platelets express extremely high concentrations (155±18 pmol/mg of membrane protein) of the most active glucose transporter isoform, GLUT3. Thrombin, a potent platelet activator, was found to stimulate 2-deoxyglucose transport activity 3-5-fold within 10 min at 25 °C, with a half-time of 1-2 min. To determine the mechanism underlying the increase in glucose transport activity, an impermeant photolabel, [2-3H]2N-4-(1-azi-2,2,2-trifluoethyl)benzoyl-1,3,-bis-(d-mannose-4-ylozy)-2-propylamine, was used to covalently bind glucose transporters accessible to the extracellular milieu. In response to thrombin, the level of transporter labelling increased 2.7-fold with a half-time of 1-2 min. This suggests a translocation of GLUT3 transporters from an intracellular site to the plasma membrane in a manner analogous to that seen for the ...

Pharmacology, 1998

The effect of continuous intracerebroventricular (i.c.v.) infusion of oxytocin (OT) on the releas... more The effect of continuous intracerebroventricular (i.c.v.) infusion of oxytocin (OT) on the release of OT and vasopressin (VP) following osmotic stimulation was studied in ovariectomized rats treated peripherally with gonadal steroids to simulate late gestation/lactation. Artificial cerebrospinal fluid (CSF) with or without OT (2 ng/µg) was infused (0.5 µl/h) i.c.v. continuously for 7 days along with sequential peripheral administration of progesterone (2 mg/kg i.m.) for 4 days, then 17-β-estradiol (200 µg/kg i.m.) for 2 days. Following 7 days of OT infusion, isotonic (0.15 mol/l NaCl) or hypertonic (1.5 mol/l NaCl) saline was injected (15 ml/kg s.c.); the animals were decapitated 1 h later. Animals infused centrally with OT had higher basal levels of OT in plasma (p < 0.01 vs. CSF). While osmotic stimulation increased plasma levels of both OT and VP (0.15 mol/l NaCl < 1.5 mol/l NaCl; p < 0.01), only circulating VP was enhanced further (p < 0.01) in animals infused with O...

Journal of Neurochemistry, 2002

: The transport of glucose across the blood‐brain barrier (BBB) is mediated by the high molecular... more : The transport of glucose across the blood‐brain barrier (BBB) is mediated by the high molecular mass (55‐kDa) isoform of the GLUT1 glucose transporter protein. In this study we have utilized the tritiated, impermeant photolabel 2‐N‐[4‐(1‐azi‐2,2,2‐trifluoroethyl)[2‐3H]propyl]‐1,3‐bis(d‐mannose‐4‐yloxy)‐2‐propylamine to develop a technique to specifically measure the concentration of GLUT1 glucose transporters on the luminal surface of the endothelial cells of the BBB. We have combined this methodology with measurements of BBB glucose transport and immunoblot analysis of isolated brain microvessels for labeled luminal GLUT1 and total GLUT1 to reevaluate the effects of chronic hypoglycemia and diabetic hyperglycemia on transendothelial glucose transport in the rat. Hypoglycemia was induced with continuous‐release insulin pellets (6 U/day) for a 12‐ to 14‐day duration ; diabetes was induced by streptozotocin (65 mg/kg i.p.) for a 14‐ to 21‐day duration. Hypoglycemia resulted in 25‐45% increases in regional BBB permeability‐surface area (PA) values for d‐[14C]glucose uptake, when measured at identical glucose concentration using the in situ brain perfusion technique. Similarily, there was a 23 ± 4% increase in total GLUT1/mg of microvessel protein and a 52 ± 13% increase in luminal GLUT1 in hypoglycemic animals, suggesting that both increased GLUT1 synthesis and a redistribution to favor luminal transporters account for the enhanced uptake. A corresponding (twofold) increase in cortical GLUT1 mRNA was observed by in situ hybridization. In contrast, no significant changes were observed in regional brain glucose uptake PA, total microvessel 55‐kDa GLUT1, or luminal GLUT1 concentrations in hyperglycemic rats. There was, however, a 30‐40% increase in total cortical GLUT1 mRNA expression, with a 96% increase in the microvessels. Neither condition altered the levels of GLUT3 mRNA or protein expression. These results show that hypoglycemia, but not hyperglycemia, alters glucose transport activity at the BBB and that these changes in transport activity result from both an overall increase in total BBB GLUT1 and an increased transporter concentration at the luminal surface.

The Journal of Membrane Biology, 1999

Journal of Cerebral Blood Flow & Metabolism, 2000

The relationship between local rates of cerebral glucose utilization (lCMRglc) and glucose transp... more The relationship between local rates of cerebral glucose utilization (lCMRglc) and glucose transporter expression was examined during physiologic activation of the hypothalamoneurohypophysial system. Three days of water deprivation, which is known to activate the hypothalamoneurohypophysial system, resulted in increased lCMRglc and increased concentrations of GLUT1 and GLUT3 in the neurohypophysis; mRNA levels of GLUT1 and GLUT3 were decreased and increased, respectively. Water deprivation also increased lCMRglc in the hypothalamic supraoptic and paraventricular nuclei; mRNA levels of GLUT1 and GLUT3 appeared to increase in these nuclei, but the changes did not achieve statistical significance. Restoration of water for 3 to 7 days reversed all observed changes in GLUT expression (protein and mRNA); restoration of water also reversed changes in lCMRglc in both the neurohypophysis and the hypothalamic nuclei. These results indicate that under conditions of neural activation and recove...