Biomedical subjects

Larry Wheeler

Publications and source records attributed to Larry Wheeler.

11 recordsLinked to original sources

PubMed2006

The prevention of colitis by E Prostanoid receptor 4 agonist through enhancement of epithelium survival and regeneration.

Inflammatory bowel disease (IBD) is often triggered and/or exacerbated by nonsteroidal anti-inflammatory drugs (NSAIDs). Among various prostanoids affected by NSAIDs, prostaglandin E2 (PGE2), in particular, seems to play critical roles in IBD via the EP4 receptor, one of the four PGE2 receptor subtypes (EP1-4). An EP4 agonist, [[3-[[(1R,2S,3R)-3-hydroxy-2-[(1E,3S)-3-hydroxy-4-[3-(methoxymethyl)phenyl]-1-butenyl]-5-oxocyclopentyl]thio]propyl]thio]-acetic acid, C22H30O6S2 (ONO-AE1-329), for example, when topically applied, has been reported to ameliorate typical colitis symptoms by suppressing the production of cytotoxic cytokines in the dextran sodium sulfate (DSS)-induced colitis model. EP4 agonists are also known, however, for their ability to protect epithelial cells from apoptosis in vitro, which may contribute to the protection of mucosal barrier functions. To investigate this potential application, we have tested another EP4-selective agonist in the DSS-indomethacin mouse colitis model. 7-[2-(3-Hydroxy-4-phenyl-but-1-enyl)-6-oxo-piperidin-1-yl]-heptanoic acid methyl ester, C23H33NO4 (AGN205203), an analog from the 8-azapiperidinone series of EP4 agonists, is metabolically and chemically more stable than the ONO agonist, because of its lack of oxidizable sulfur atoms in the alpha-chain and of 11-OH group, a potential source of beta-elimination reaction. Treatment of mice subcutaneously with AGN205203 at 3 mg/kg/day minimized colitis symptoms, such as weight loss, diarrhea, and colonic bleeding. Further histological examination of colons revealed healthy surface columnar epithelial cells free of erosion and ulceration compared with those without the drug treatment. At cellular level, the drug treatment decreased colon epithelial apoptosis, prevented goblet cell depletion, and promoted epithelial regeneration. AGN205203 may be unique among known EP4 agonists for its metabolic and chemical stability, and it is amenable to systemic applications for the prevention and recovery of IBD.

Animals↗

PubMed2006

Ocular changes after photodynamic therapy.

PURPOSE: The aim of this study was to identify the changes in the primate visual system after a single session of photodynamic therapy (PDT) in an intact nonhuman primate retina. METHODS: As part of a larger study, PDT (wavelength 689 nm, 50 J/cm2, 600 mW/cm2, 83 seconds, 4-mm spot size) with verteporfin (6 mg/m2 intravenous infusion) was performed in one eye each of two cynomolgus monkeys. Fundus photography, fluorescein angiography (FA), indocyanine green angiography (ICG), optical coherence tomography (OCT), and multifocal electroretinography (mfERG) were performed at baseline and 12 time points (1-283 days) after PDT. In addition, retinal histopathologic findings were evaluated at 9 months. RESULTS: Various morphologic changes, including whitening of the treated area, RPE proliferation, closure of the choroidal vasculature, and subretinal edema (followed by foveolar thinning) were observed. Most of the changes persisted and were detectable in histopathologic evaluation at 9 months. Reductions of the mfERG amplitude, followed by varying degrees of recovery from the treated and the border regions, were observed. This was accompanied by progressive delay of P1 peak time up to 3 months after treatment, followed by complete recovery at 9 months. In addition, the nontreated area showed amplitude and timing mfERG deficits, which underwent gradual (but not complete) recovery. CONCLUSIONS: In a primate model, under standard clinical parameters, a single PDT treatment resulted in various dynamic morphologic and functional retinal changes detectable for up to 9 months after treatment. The significance of the observed changes and possible ways of pharmacologic interference with PDT adverse effects are discussed.

Animals↗

PubMed2005

T-cell-based vaccination for morphological and functional neuroprotection in a rat model of chronically elevated intraocular pressure.

Acute or chronic glaucoma is often associated with an increase in intraocular pressure (IOP). In many patients, however, therapeutic pressure reduction does not halt disease progression. Neuroprotection has been proposed as a complementary therapeutic approach. We previously demonstrated effective T-cell-based neuroprotection in experimental animals vaccinated with the synthetic copolymer glatiramer acetate (copolymer-1, Cop-1), a weak agonist of self-antigens. This study was undertaken to test different routes and modes of vaccination with Cop-1 as treatment modalities for protection against retinal ganglion cell (RGC) death caused by chronic elevation of IOP in rats, and to determine whether anatomical neuroprotection is accompanied by functional neuroprotection. In a chronic model of unilaterally high IOP, Cop-1 vaccination, with or without an adjuvant, protected rats against IOP-induced loss of RGCs by eliciting a systemic T-cell-mediated response capable of cross-reacting with self-antigens residing in the eye. In rats deprived of T cells, Cop-1 (unlike treatment with alpha2-adrenoreceptor agonists) was not protective of RGCs, substantiating the contention that its beneficial effect is not conferred directly but is T-cell-mediated. Pattern electroretinography provided evidence of functional protection. Thus, vaccination with adjuvant-free Cop-1 can protect RGCs from the consequences of elevated IOP in rats. This protection is manifested both morphologically and functionally. These findings can be readily implemented for the development of a therapeutic vaccination to arrest the progression of glaucoma.

Adjuvants, Immunologic↗

PubMed2005

Studies using isolated uterine and other preparations show bimatoprost and prostanoid FP agonists have different activity profiles.

1. The pharmacology of bimatoprost, a synthetic prostaglandin-amide, was examined in prostaglandin F(2alpha) (PGF(2alpha))-sensitive preparations. Bimatoprost potently contracted the rabbit isolated uterus (pEC(50)=7.92+/-0.16). In contrast, bimatoprost exhibited weak excitatory activity in human myometrium from pregnant and nonpregnant donors, mouse uterus, rat uterus, and endothelium-intact rabbit jugular veins, and did not stimulate DNA synthesis in mouse fibroblasts. 2. The possibility that the effects of bimatoprost may reflect partial agonism at prostanoid FP receptors was examined and the contractile effects of full agonists, 17-phenyl PGF(2alpha) (FP) and U-46619 (TP, a control), were determined in the absence and presence of 1 muM bimatoprost on the mouse uterus. Analyses of the agonist-agonist functional studies showed no antagonism, indicating that bimatoprost is not a partial agonist. 3. Bioassay metabolism studies of bimatoprost and latanoprost (FP receptor agonist prodrug) in the rabbit uterus were conducted using recipient mouse uterus. Results indicated that the potent responses to bimatoprost in the rabbit uterus are produced by the intact molecule and not by its putative free acid metabolite, 17-phenyl PGF(2alpha). Some hydrolysis of latanoprost to latanoprost free acid appears to have occurred in the rabbit uterus, according to biological detection. 4. The pharmacology of bimatoprost could not be explained by its interaction with known prostanoid FP receptors and was independent of species-, tissue-, or preparation-related factors. The potent contractile effects of bimatoprost in the rabbit uterus provide further pharmacological evidence for the presence of a novel receptor population that preferentially recognises bimatoprost.

3T3 Cells↗

PubMed2005

Effect of bimatoprost on intraocular pressure in prostaglandin FP receptor knockout mice.

PURPOSE: To determine the effect of bimatoprost on intraocular pressure in the prostaglandin FP receptor knockout mouse. METHODS: The IOP response to a single 1.2-microg (4 microL) dose of bimatoprost was measured in the treated and untreated fellow eyes of homozygote (FP+/+, n = 9) and heterozygote (FP+/-, n = 10) FP-knockout mice, as well as in wild-type C57BL/6 mice (FP+/+, n = 20). Serial IOP measurements were also performed after topical bimatoprost in a separate generation of homozygous FP-knockout mice and wild-type littermate control animals (n = 4 per group). Aqueous humor protein concentrations were measured to establish the state of the blood-aqueous barrier. Tissue, aqueous humor and vitreous concentrations of bimatoprost, latanoprost, and their C-1 free acids were determined by liquid chromatography and tandem mass spectrometry. RESULTS: A significant reduction in IOP was observed in the bimatoprost-treated eye of wild-type mice at 2 hours, with a mean difference and 95% confidence interval (CI) of the difference in means of -1.33 mm Hg (-0.81 to -1.84). Bimatoprost did not lead to a significant reduction in IOP in either the heterozygous knockout -0.36 mm Hg (-0.82 to +0.09) or homozygous FP-knockout mice 0.25 mm Hg (-0.38 to +0.89). The lack of an IOP response in the FP-knockout mice was not a consequence of blood-aqueous barrier breakdown, as there was no significant difference in aqueous humor protein concentration between treated and fellow eyes. Tissue and aqueous humor concentrations of bimatoprost, latanoprost, and their C-1 free acids indicate that latanoprost, but not bimatoprost, is hydrolyzed in the mouse eye after topical administration. CONCLUSIONS: An intact FP receptor gene is critical to the IOP response to bimatoprost in the mouse eye.

Amides↗

PubMed2004

Efficacy and safety of memantine treatment for reduction of changes associated with experimental glaucoma in monkey, I: Functional measures.

PURPOSE: To determine, using electrophysiological measures of visual system function, whether oral daily dosing of memantine is both safe and effective to reduce the injury associated with experimental glaucoma in primates. METHODS: Argon laser treatment of the anterior chamber angle was used to induce chronic ocular hypertension (COHT) in the right eye of 18 macaque monkeys. Nine animals were orally dosed daily with 4 mg/kg memantine while the other nine animals received an oral dose of vehicle only. Using both conventional and multifocal methods, recordings of the electroretinogram (ERG) were made at approximately 3, 5, and 16 months after elevation of the intraocular pressure (IOP). Recordings of the visually-evoked cortical potential (VECP) were also made at the 16-month time point. RESULTS: Chronic ocular hypertension was associated with a reduction in the amplitude of components of the multifocal ERG response and visually-evoked cortical potential. Memantine-treated animals suffered less amplitude reduction for these measures than did vehicle-treated animals, though this treatment effect on the ERG measures was observed only at the early time points (3 and 5 months post IOP elevation). Memantine treatment was not associated with an effect on either the kinetics or amplitude of ERG or VECP response measures obtained from the normotensive eyes. CONCLUSIONS: Systemic treatment with memantine, a compound which does not lower intraocular pressure, was both safe and effective for reduction of functional loss associated with experimental glaucoma.

Administration, Oral↗

PubMed2004

Efficacy and safety of memantine treatment for reduction of changes associated with experimental glaucoma in monkey, II: Structural measures.

PURPOSE: To determine, using anatomic measurements, whether daily oral dosing with memantine is both safe and effective to reduce the injury associated with experimental glaucoma in primates. METHODS: Argon laser treatment of the anterior chamber angle was used to induce chronic ocular hypertension (COHT) in the right eyes of 18 macaque monkeys. Nine animals were daily orally dosed with 4 mg/kg memantine while the other nine animals received vehicle only. Measurements of intraocular pressure (IOP) from both eyes of all animals were made at regular intervals. Appearance of the optic nerve head, retinal vessels, and surrounding retina was documented with stereo fundus photographs obtained at multiple time points throughout the study. Measurements of optic nerve head topography were obtained from confocal laser scans made from animals with the highest IOPs at approximately 3, 5, and 10 months after elevation of IOP. At approximately 16 months after IOP elevation, animals were killed and histologic counts of cells in the retinal ganglion cell (RGC) layer were made. RESULTS: Histologic measurements showed that, for animals with moderate elevation of IOP, memantine treatment was associated with an enhanced survival of RGCs in the inferior retina. Measurements of optic nerve head topography showed less IOP-induced change in memantine-treated animals. This effect was seen in measurements of both the cup and the neuroretinal rim. A comparison of these same histologic and morphologic measurements in normotensive eyes from the two treatment groups showed that memantine treatment was not associated with any significant effects on these eyes. CONCLUSIONS: Histologic measurements of RGC survival as well as tomographic measurements of nerve head topography show that systemic treatment with memantine, a compound which does not lower intraocular pressure, is both safe and effective to reduce changes associated with experimental glaucoma.

Administration, Oral↗

PubMed2003

Role of alpha-2 agonists in neuroprotection.

Four criteria are used to evaluate the potential usefulness of an agent for neuroprotection in glaucoma: 1) the agent must have a target in the retina; 2) it must be neuroprotective in animal models; 3) it must reach neuroprotective concentrations in the posterior segment after clinical dosing; and finally, 4) it must be shown to be neuroprotective in clinical trials. The alpha-2 adrenergic agonist brimonidine has met the first three criteria and clinical trials to establish the fulfillment of the fourth criterion are ongoing. The effects of brimonidine are mediated by its interaction with alpha-2 adrenergic receptors that are present in the retina. Activation of alpha-2 receptors by brimonidine has been shown to effectively promote the survival and function of retinal ganglion cells in a variety of animal models of optic injury relevant to glaucoma such as the chronic ocular hypertensive rat and rat optic nerve crush. Brimonidine has also been shown to be neuroprotective in the rat ischemia reperfusion model that evaluates general hypoxic damage to the whole retina. Clinical dosing of the topical formulation of brimonidine results in brimonidine concentrations in the posterior segment that are sufficient for both pharmacological activity at alpha-2 adrenergic receptors and neuroprotection. Finally, clinical trials are in progress to investigate the ability of brimonidine to protect human retinal ganglion cells and the visual field in glaucoma-related disease.

Adrenergic alpha-2 Receptor Agonists↗

PubMed2003

Hypothesis for a common basis for neuroprotection in glaucoma and Alzheimer's disease: anti-apoptosis by alpha-2-adrenergic receptor activation.

Recent studies have suggested glaucomatous loss of retinal ganglion cells and their axons in Alzheimer's disease. Amyloid beta peptides and phosphorylated tau protein have been implicated in the selective regional neuronal loss and protein accumulations characteristic of Alzheimer's disease. Similar protein accumulations are not present on glaucomatous retinal ganglion cells. Neurons die in both Alzheimer's disease and glaucoma by apoptosis, although the signaling pathways for neuronal degradation appear to differ in the two diseases. Alzheimer's disease features a loss of locus ceruleus noradrenergic neurons, which send axon terminals to the brain regions suffering neuronal apoptosis and results in reductions in noradrenaline in those regions. Activation of alpha-2 adrenergic receptors reduces neuronal apoptosis, in part through a protein kinase B (Akt)-dependent signaling pathway. Loss of noradrenaline innervation facilitates neuronal apoptosis in Alzheimer's disease models and may act similarly in glaucoma. Alpha-2 adrenergic receptor agonists offer the potential to slow the neuronal loss in both diseases by compensating for lost noradrenaline innervation.

Adrenergic alpha-Agonists↗

PubMed2002

Distribution of brimonidine into anterior and posterior tissues of monkey, rabbit, and rat eyes.

The objectives of the study were to evaluate the distribution of brimonidine (alpha2-adrenergic agonist) into anterior and posterior ocular tissues. Single or multiple doses of a 0.2 or 0.5% brimonidine tartrate solution were administered to one or both eyes of monkeys or to one eye of rabbits. Brimonidine was administered intraperitoneally to rats. After topical administration, [14C]brimonidine was rapidly absorbed into the cornea and conjunctiva and distributed throughout the eye. [14C]Radioactivity was higher and cleared more slowly in pigmented tissues (iris/ciliary body, choroid/retina, and optic nerve) than in nonpigmented tissues. Single and multiple dosing led to a similar drug distribution, with higher levels of brimonidine measured in pigmented tissues after multiple dosing. Most of the radioactivity extracted from ocular tissues represented unchanged brimonidine. In the rabbits and the monkey treated in only one eye, levels of radioactivity in the untreated eye were low, consistent with the low systemic levels and rapid drug clearance. Posterior ocular tissue concentrations of radioactivity exceeded systemic blood concentrations. The vitreous humor brimonidine concentrations in monkeys treated topically with 0.2% brimonidine tartrate was 82 +/- 45 nM. Vitreous levels in rabbits confirmed the penetration of brimonidine to the posterior segment. Similar concentrations of brimonidine (22 to 390 nM) were measured in the vitreous and retina of rats injected intraperitoneally with brimonidine. Both topically applied and systemically administered brimonidine reach the back of the eye at nanomolar concentrations sufficient to activate alpha2-adrenergic receptors. The brimonidine levels achieved at the retina are relevant for neuroprotection models.

Administration, Topical↗

PubMedDate not supplied

Alpha-2 adrenoceptor agonist protects retinal function after acute retinal ischemic injury in the rat.

Alpha-2 adrenoceptor agonists have previously been shown to enhance neuronal survival in an optic nerve mechanical injury model and to protect photoreceptors in a light-induced degeneration model. The purpose of this study was to examine the effect of the alpha-2 adrenoceptor agonist in a pressure-induced retinal ischemia model. Brown-Norway rats were treated systemically or topically with alpha-2 adrenoceptor specific agonist brimonidine. Retinal ischemia was induced by increasing the intraocular pressure to 110 mm Hg for 50 min. The effect of brimonidine on retinal ischemic injury was functionally assessed in the rats 7 d later using electroretinography (ERG). Ischemia-induced retinal cell death was studied using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining. We found that brimonidine treatment significantly protected the retina from retinal ischemic injury in a dose- and time-dependent manner. This protection can be achieved either by systemic or topical application and can be blocked by pretreatment with the alpha-2 adrenoceptor antagonist, yohimbine. Using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analysis, we found that brimonidine can up-regulate the expression of basic fibroblast growth factor, bcl-2 and bcl-xl in the retina. The drug also can activate two major cell survival signaling pathways in the retina: the extracellular-signal-regulated kinases (ERKs) and phosphatidylinositol-3' kinase/protein kinase Akt pathways. All these aforementioned factors may potentially contribute in mediating brimonidine's protective effect in this acute retinal ischemia model.

Adrenergic alpha-2 Receptor Agonists↗