SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Aqueous humour

163

Numerous studies have been completed on glaucoma pathogenesis. However, the potential and controversial interaction between ocular biomechanical properties and the glaucomatous diseases process has received much more attention recently. Previous studies have found that collagen tissues gain mutation change in glaucoma patients. This study was conducted to determine the role of collagen in the biomechanics of glaucoma in humans. Its changes may be the result of mechanical modifications brought on by intraocular pressure (IOP) fluctuations. More importantly, biomechanics and genetic evidence indicate that the mutation of collagen may play a role in the process of glaucoma. Alteration of collagen in the outflow pathway may alter mechanical tissue characteristics and a concomitant increase of aqueous humor outflow resistance and elevation of IOP. The variations of collagen, leading to inter-individual differences in scleral and lamina cribrosa properties, result in different susceptibility of individuals to elevated IOP. Therefore, this study hypothesized that collagen mutations may be an original cause of glaucoma.

Concepts: Bone, Genetics, Mutation, Cartilage, Cornea, Intraocular pressure, Biomechanics, Aqueous humour

50

Limited training, high cost, and low equipment mobility leads to inaccuracies in decision making and is concerning with serious ocular injuries such as suspected ruptured globe or post-operative infections. Here, we present a novel point-of-service (POS) quantitative ascorbic acid (AA) assay with use of the OcuCheck Biosensor. The present work describes the development and clinical testing of the paper-based biosensor that measures the changes in electrical resistance of the enzyme-plated interdigitated electrodes to quantify the level of AA present in ocular fluid. We have demonstrated the proof-of-concept of the biosensor testing 16 clinical samples collected from aqueous humor of patients undergoing therapeutic anterior chamber paracentesis. Comparing with gold standard colorimetric assay for AA concentration, OcuCheck showed accuracy of >80%, sensitivity of >88% and specificity of >71%. At present, there are no FDA-approved POS tests that can directly measures AA concentration levels in ocular fluid. We envisage that the device can be realized as a handheld, battery powered instrument that will have high impact on glaucoma care and point-of-care diagnostics of penetrating ocular globe injuries.

Concepts: Present, Decision making, Acid, Electric current, Electrochemistry, Battery, Aqueous humour, Ascorbic acid

45

Most medications targeting optic neuropathies are administered as eye drops. However, their corneal penetration efficiencies are typically < 5%. There is a clear, unmet need for novel transcorneal drug delivery vehicles. To this end, we have developed a stimulus-responsive, in situ-forming, nanoparticle-laden hydrogel for controlled release of poorly bioavailable drugs into the aqueous humor of the eye. The hydrogel is formulated as a composite of hyaluronic acid (HA) and methylcellulose (MC). The amphiphilic nanoparticles are composed of poly(ethylene oxide) (PEO) and poly(lactic acid) (PLA). Experimental design aided the identification of hydrogel composition and nanoparticle content in the formulation, and the formulation reliably switched between thixotropy and temperature-dependent rheopexy when it was tested in a rheometer under conditions that simulate the ocular surface, including blinking. These properties should ensure that the formulation coats the cornea through blinking of the eyelid and facilitate application of the medication as an eye drop immediately prior to the patient's bedtime. We subsequently tested the efficacy of our formulation in whole-eye experiments by loading the nanoparticles with cannabigerolic acid (CBGA). Our formulation exhibits over a 300% increase in transcorneal penetration over control formulations. This work paves the way for the introduction of novel products targeting ocular diseases to the market.

Concepts: Pharmacology, Drug, Drugs, Eye, Cornea, Pharmaceutical drug, Aqueous humour, Carboxymethyl cellulose

28

In this work, we aim to design and synthesize prodrugs of gatifloxacin targeting organic cation transporter (OCT), monocarboxylate transporter (MCT), and ATB (0, +) transporters and to identify a prodrug with enhanced delivery to the back of the eye. Dimethylamino-propyl, carboxy-propyl, and amino-propyl(2-methyl) derivatives of gatifloxacin (GFX), DMAP-GFX, CP-GFX, and APM-GFX, were designed and synthesized to target OCT, MCT, and ATB (0, +) transporters, respectively. An LC-MS method was developed to analyze drug and prodrug levels in various studies. Solubility and log D (pH 7.4) were measured for prodrugs and the parent drug. The permeability of the prodrugs was determined in the cornea, conjunctiva, and sclera-choroid-retinal pigment epitheluim (SCRPE) and compared with gatifloxacin using an Ussing chamber assembly. Permeability mechanisms were elucidated by determining the transport in the presence of transporter specific inhibitors. 1-Methyl-4-phenylpyridinium iodide (MPP+), nicotinic acid sodium salt, and α-methyl-dl-tryptophan were used to inhibit OCT, MCT, and ATB (0, +) transporters, respectively. A prodrug selected based on in vitro studies was administered as an eye drop to pigmented rabbits, and the delivery to various eye tissues including vitreous humor was compared with gatifloxacin dosing. DMAP-GFX exhibited 12.8-fold greater solubility than GFX. All prodrugs were more lipophilic, with the measured log D (pH 7.4) values ranging from 0.05 to 1.04, when compared to GFX (log D: -1.15). DMAP-GFX showed 1.4-, 1.8-, and 1.9-fold improvement in permeability across the cornea, conjunctiva, and SCRPE when compared to GFX. Moreover, it exhibited reduced permeability in the presence of MPP+ (competitive inhibitor of OCT), indicating OCT-mediated transport. CP-GFX showed 1.2-, 2.3-, and 2.5-fold improvement in permeability across the cornea, conjunctiva, and SCRPE, respectively. In the presence of nicotinic acid (competitive inhibitor of MCT), the permeability of CP-GFX was reduced across the conjunctiva. However, the cornea and SCRPE permeability of CP-GFX was not affected by nicotinic acid. APM-GFX did not show any improvement in permeability when compared to GFX across the cornea, conjunctiva, and SCRPE. Based on solubility and permeability, DMAP-GFX was selected for in vivo studies. DMAP-GFX showed 3.6- and 1.95-fold higher levels in vitreous humor and CRPE compared to that of GFX at 1 h after topical dosing. In vivo conversion of DMAP-GFX prodrug to GFX was quantified in tissues isolated at 1 h after dosing. The parent drug-to-prodrug ratio was 8, 70, 24, 21, 29, 13, 55, and 60% in the cornea, conjunctiva, iris-ciliary body, aqueous humor, sclera, CRPE, retina, and vitreous humor, respectively. In conclusion, DMAP-GFX prodrug enhanced solubility, log D, as well as OCT mediated delivery of gatifloxacin to the back of the eye.

Concepts: In vivo, Retina, Eye, Enzyme inhibitor, Cornea, In vitro, Aqueous humour, Prodrug

27

The purpose of this study was to explore a composite thermosensitive in situ gelling formulation using the distribution of solid lipid nanoparticles (SLNs) among poloxamer-based hydrogels as a potential carrier for novel ocular drug delivery. SLNs containing the model drug Resina Draconis were prepared using a melt-emulsion ultrasonication method. A central composite design (CCD) was adopted to screen the thermosensitive hydrogel (THG) formulation. After aqueous SLNs were dispersed into the THG matrices, the physicochemical properties of the SLNs were characterized before and after their incorporation into hydrogels. The in vitro corneal penetration experiment, ocular irritant test and transcorneal mechanism across the cornea have been previously described to predict the feasibility for the proposed ophthalmic application. Finally, the optimal THGs consisted of 27.8% (w/v) poloxamer 407 and 3.55% (w/v) poloxamer 188. The particle size of the SLNs remained within the colloidal range. In vitro corneal penetration studies revealed a nearly steady sustained drug release. The hen’s egg test-chorioallantoic membrane (HET-CAM) test indicated that all of the tested polymer systems were non-irritant. Coumarin-6 labeled SLNs formulated into THGs displayed a more homogeneous fluorescence with a deeper penetration intensity into the cornea at various times. Taken together, these results suggest that the SLN-based THG system can be used as a potential vehicle for ocular application.

Concepts: Sol-gel, Cornea, In vitro, Physical chemistry, In situ, Solution, Aqueous humour, Poloxamer 407

23

To analyze cytokine profiles of the aqueous humor of eyes with primary open-angle glaucoma (POAG), neovascular glaucoma (NVG), and cataract (as controls).

Concepts: Cytokine, Glaucoma, Aqueous humour

8

Primary open-angle glaucoma (POAG) is often caused by elevated intraocular pressure (IOP), which arises due to increased resistance to aqueous humor outflow (AHO). Aqueous humor flows through Schlemm’s canal (SC), a lymphatic-like vessel encircling the cornea, and via intercellular spaces of ciliary muscle cells. However, the mechanisms underlying increased AHO resistance are poorly understood. Here, we demonstrate that signaling between angiopoietin (Angpt) and the Angpt receptor Tie2, which is critical for SC formation, is also indispensable for maintaining SC integrity during adulthood. Deletion of Angpt1/Angpt2 or Tie2 in adult mice severely impaired SC integrity and transcytosis, leading to elevated IOP, retinal neuron damage, and impairment of retinal ganglion cell function, all hallmarks of POAG in humans. We found that SC integrity is maintained by interconnected and coordinated functions of Angpt-Tie2 signaling, AHO, and Prox1 activity. These functions diminish in the SC during aging, leading to impaired integrity and transcytosis. Intriguingly, Tie2 reactivation using a Tie2 agonistic antibody rescued the POAG phenotype in Angpt1/Angpt2-deficient mice and rejuvenated the SC in aged mice. These results indicate that the Angpt-Tie2 system is essential for SC integrity. The impairment of this system underlies POAG-associated pathogenesis, supporting the possibility that Tie2 agonists could be a therapeutic option for glaucoma.

Concepts: Retina, Eye, Intraocular pressure, Glaucoma, Aqueous humour, Retinal ganglion cell, Trabecular meshwork, Ciliary body

5

Glaucoma is a leading cause of blindness, afflicting more than 60 million people worldwide. Increased intraocular pressure (IOP) due to impaired aqueous humor drainage is a major risk factor for the development of glaucoma. Here, we demonstrated that genetic disruption of the angiopoietin/TIE2 (ANGPT/TIE2) signaling pathway results in high IOP, buphthalmos, and classic features of glaucoma, including retinal ganglion degeneration and vision loss. Eyes from mice with induced deletion of Angpt1 and Angpt2 (A1A2FloxWB mice) lacked drainage pathways in the corneal limbus, including Schlemm’s canal and lymphatic capillaries, which share expression of the PROX1, VEGFR3, and FOXC family of transcription factors. VEGFR3 and FOXCs have been linked to lymphatic disorders in patients, and FOXC1 has been linked to glaucoma. In contrast to blood endothelium, in which ANGPT2 is an antagonist of ANGPT1, we have shown that both ligands cooperate to regulate TIE2 in the lymphatic network of the eye. While A1A2FloxWB mice developed high IOP and glaucoma, expression of ANGPT1 or ANGPT2 alone was sufficient for ocular drainage. Furthermore, we demonstrated that loss of FOXC2 from lymphatics results in TIE2 downregulation, suggesting a mechanism for ocular defects in patients with FOXC mutations. These data reveal a pathogenetic and molecular basis for glaucoma and demonstrate the importance of angiopoietin ligand cooperation in the lymphatic endothelium.

Concepts: DNA, Eye, Cornea, Intraocular pressure, Glaucoma, Ophthalmology, Aqueous humour, Blindness

3

Retinoblastoma (Rb) is one of the first tumors to have a known genetic etiology. However, because biopsy of this tumor is contraindicated, it has not been possible to define the effects of secondary genetic changes on the disease course.

Concepts: Cancer, Genetic disorder, Medical terms, Brain tumor, Tumor, Aqueous humour

3

Iontophoresis of nanocarriers in the eye has been proposed to sustain drug delivery and maintain therapeutic concentrations. Fourth generation polyamidoamine (PAMAM) dendrimers are semi-rigid nanoparticles with surface groups that are easily modified. These dendrimers are known to modulate tight junctions, increase paracellular transport of small molecules and be translocated across epithelial barriers, exhibiting high uptake by different cell lines. The first aim of this study was to investigate the effect of iontophoresis on PAMAM penetration and distribution into the cornea. The second aim was to evaluate, ex vivo and in vivo, the effect of these dendrimers in dexamethasone (Dex) transcorneal iontophoresis. Anionic (PAMAM G3.5) and cationic (PAMAM G4) dendrimers were labeled with fluorescein isothiocyanate (FITC), and their distribution in the cornea was investigated using confocal microscopy after ex vivo anodal and cathodal iontophoresis for various application times. The particle size distribution and zeta potential of the dendrimers in an isosmotic solution was determined using dynamic light scattering and nanoparticle tracking analysis (NTA), where the movement of small particles and the formation of large aggregates, from 5 to 100nm, could be observed. Transcorneal iontophoresis increased the intensity and depth of PAMAM-FITC fluorescence in the cornea, suggesting improved transport of the dendrimers across the epithelium toward the stroma. PAMAM complexes with Dex were characterized by (13)C-NMR, (1)H-NMR and DOSY. PAMAM G3.5 and PAMAM G4 increased the aqueous solubility of Dex by 10.3 and 3.9-fold, respectively; however, the particle size distribution and zeta potential remained unchanged. PAMAM G3.5 decreased the Dex diffusion coefficient 48-fold compared with PAMAM G4. The ex vivo studies showed that iontophoresis increased the amount of Dex that penetrated into the cornea by 2.9, 5.6 and 3.0-fold for Dex, Dex-PAMAM G4 and Dex-PAMAM G3.5, respectively. In vivo experiments, however, revealed that iontophoresis of Dex-PAMAM-G3.5 increased Dex concentration in the aqueous humor by 6.6-fold, while iontophoresis of Dex-PAMAM G4 and Dex increased it 2.5 and 2-fold, respectively. Therefore, iontophoresis targeted PAMAM to the cornea but it is the sustained delivery of the Dex from PAMAM that prevents its rapid elimination from the aqueous humor. In conclusion, iontophoresis of PAMAM complexes represents a promising strategy for targeted and sustained topical drug delivery to the eye.

Concepts: Concentration, Epithelium, In vivo, Eye, Cornea, Particle size distribution, Aqueous humour, Colloidal chemistry