An ultrastructural study of complex carbohydrates in the posterior chamber and vitreous base of the mouse

Morphology and Composition of the Inner Limiting Membrane: Species-Specific Variations and Relevance toward Drug Delivery Research

The inner limiting membrane (ILM) represents the structural boundary between the vitreous and the retina, and is suggested to act as a barrier for a wide range of retinal therapies. While it is widely acknowledged that the morphology of the human ILM exhibits regional variations and undergoes age-related changes, insight into its structure in laboratory animals is very limited. Besides presenting a detailed overview of the morphology and composition of the human ILM, this review specifically reflects on the species-specific differences in ILM structure. With these differences in mind, we furthermore summarize the most relevant reports on the barrier role of the ILM with regard to viral vectors, nanoparticles, anti-VEGF medication and stem cells. Overall, this review aims to deliberate on the impact of species-specific ILM variations on drug delivery research as well as to pinpoint knowledge gaps which future basic research should resolve.

Proteoglycans associated with the ciliary zonule of the rat eye: a histochemical and immunocytochemical study

The structural organization of integral and associated components of the ciliary zonule is still not fully understood. The present study is to localize and characterize the proteoglycans associated with the ciliary zonule of the rat eye by Cuprolinic blue (CB) staining and immunocytochemistry. After CB staining, the proteoglycans appeared as electron dense elongated rodlets and were localized with the zonular fibers. They were seen lying on the periphery of the zonular fibers or along the length of the individual fibrils. Most of the CB rodlets had a size of 60-170 nm long (average 130 nm) and 25 nm wide. Smaller CB rodlets measuring 25-60 nm long (average 45 nm) and 12 nm wide were sometimes found associated with the individual zonular fibrils. The CB rodlets were removed after chondroitinase ABC or chondroitinase AC treatment, but were resistant to heparitinase, nitrous acid, keratanase or Streptomyces hyaluronidase digestions. The ciliary zonule was also immunostained with three monoclonal antibodies: 2-B-6 specific for chondroitin 4-sulfate, 3-B-3 for chondroitin 6-sulfate and 1-B-5 for unsulfated chondroitin, using indirect immunoperoxidase or immuno-colloidal gold methods. The zonular fibers were immunoperoxidase stained and immunogold labeled by 2-B-6, but were not reactive to 3-B-3 and 1-B-5. The results demonstrate that chondroitin sulfate proteoglycan is associated with the ciliary zonule of the rat eye.

Partial characterization, origin and turnover of glycoproteins of the rabbit vitreous body

L-[3H]fucose was injected intravitreally into rabbits that were killed from 1 hr to 28 days after injection. The vitreous bodies were processed for radiometric techniques, and electrophoresis followed by fluorography. Unbound [3H]fucose remained at a high level up to 1 day, whereas the peak of [3H]fucose bound to glycoproteins was observed at 3 days after injection with a continuous decrease afterwards. The turnover rate of vitreous glycoproteins was estimated at 4.37% per day and their turnover time at 22.85 days. Electrophoresis and fluorography combined revealed about 14 bands of glycoproteins with fucose residues and there were strong indications of differences in turnover rate among individual glycoproteins. The most prominent band in the Coomassie blue-stained gels was the one having a molecular weight of 69 kDa and it was not labeled with [3H]fucose. This band was tentatively identified as serum albumin. On the other hand, the 14 bands labeled with [3H]fucose were glycoproteins originating from within the eye, that is, they are intrinsic constituents of the vitreous body.

Proteoglycan biosynthesis by chick embryo retina glial-like cells

In this report we present biochemical evidence that purified cultures of chick embryo retina glial-like cells actively synthesize heparan sulfate (HS) and chondroitin sulfate/dermatan sulfate (CS/DS) proteoglycans as well as hyaluronic acid. Glial-like cell cultures were metabolically labeled with [3H]glucosamine and 35SO4, and the medium, cell layer, and substratum-bound fractions were analyzed separately. Proteoglycans were characterized according to charge, apparent molecular size, and glycosaminoglycan (GAG) composition and were found to be differentially distributed among the cellular compartments. HS was the predominant GAG overall and was the major species found in the cell layer and substratum-bound fractions. CS/DS was also present in each fraction and comprised the largest proportion of GAGs in the medium. The major GAG-containing material resolved into three different size classes. The first, found in the cell layer and substratum-bound fractions, contained both CS/DS and HS and was of large size. A second, intermediately sized class with a higher CS/DS:HS ratio was found in the medium. The smallest class was found in the cell layer fraction and comprised HS, most likely present as free GAG chains. In addition, each fraction contained hyaluronic acid. Characteristics of these macromolecules differ from those produced by purified cultures of chick embryo retina neurons and photoreceptors in terms of size, compartmental distribution, and presence of hyaluronic acid.

Ultrastructure of complex carbohydrates of rodent and monkey ependymal glycocalyx and meninges

The surfaces of the brain offer metabolic and mechanical support to the underlying parenchyma. Mouse, rat, and monkey brains were fixed by immersion in a glutaraldehyde fixative or glutaraldehyde with cetylpyridinium chloride, followed by block staining for complex carbohydrates using alcian blue with OsO4 postfixation, or OsO4 postfixative solution containing ruthenium red, or alcian blue and then ruthenium red-OsO4 treatment. The ependyma in these species had a glycocalyx extending into the ventricular fluid as a finely filamentous network when stained with alcian blue or with alcian blue followed by ruthenium red-OsO4. Mice in the middle age range had stained material in this glycocalyx resembling the hyaluronic acid reported in the ocular vitreous body. Similar material was seen in the arachnoidal space of these mice and in the inner connective tissue matrix of the dura mater. Both the mouse and monkey had a cell-free zone, termed the inner dural matrix zone, between the thick fibrous dura and its innermost cellular layer. This zone contained filamentous and globular alcian blue-stained material. The complex carbohydrates of the mouse ependymal glycocalyx and inner dural matrix zone underwent changes developmentally. Aged rats were injected intraventricularly with latex beads, which, along with extravasated erythrocytes, were seen to adhere to the ependymal glycocalyx. A similar adhesion of erythrocytes was seen in the mouse and monkey ependymal glycocalyx and in the filamentous network of the mouse and monkey inner dural matrix zone. The ependymal glycocalyx, formed in part of complex carbohydrates, is much thicker than previously demonstrated. Some activities related to the ependymal lining of the ventricles, including the movement of cells or particles, the penetration of metabolites or serum-protein fractions (e.g., immunoglobulins), and cell-surface hydration, probably depend in part on complex carbohydrates that provide a sticky, electrically negative, hydrophilic environment. The complex carbohydrates in the inner dural matrix zone might provide mechanical buffering. Complex carbohydrates in the arachnoidal space may help to maintain a loose tissue that needs not only to be hydrated, but also to be open enough to provide cerebrospinal fluid circulation.

Synthesis and migration of 3H-fucose-labeled glycoproteins in the ciliary epithelium of the eye: effects of microtubule-disrupting drugs

3H-fucose was injected intravenously or intravitreously into albino rats. After time intervals of 10, 40, and 50 min, 1, 1.5, and 4 hr, 1, 3, and 7 days, and 1, 2, and 4 weeks after injection, the animals were sacrificed by intracardiac perfusion with glutaraldehyde. Samples of the ciliary body were prepared for light and electron microscope radioautography. Light microscope autoradiographs showed that the cells of both the inner and outer layers of ciliary epithelium actively incorporated 3H-fucose label in a reaction that peaked in intensity at 4 hr after injection, and then progressively declined. Electron microscope radioautographs revealed that, at early time intervals, most of the label was localized to the Golgi apparatus. With time, the plasma membrane of both cell types became increasingly labeled, and accounted for 60-70% of the total silver grains at 4 hr after injection. Adjacent to the basal cell surface of the inner layer cells, the fibers of the zonula became increasingly labeled from 1.5 hr onwards, providing strong evidence that these cells secrete glycoproteins to the zonula. When vinblastine was administered 30 min before 3H-fucose injection, followed by sacrifice 1.5 hr later, a much larger proportion of label remained localized to the Golgi apparatus than in controls, and the plasma membrane and zonula were much less labeled. These results suggest that, as documented in other cell types, microtubules may play a role in the intracellular transport of membrane and secretory glycoproteins in these cells.

Histochemical demonstration of hyaluronic acid molecules by alcian blue

Specimens of vitreous humour (monkey eye), Wharton jelly (human umbilical cord) and commercial hyaluronates were immersed in buffered fixative solutions containing either aldehydes and Alcian Blue, or aldehydes and Alcian Blue with MgCl2 as electrolyte. Two MgCl2 concentrations were used, 0.025 M and 0.3 M. Immersion in both solutions induced formation of precipitates which were postfixed in OsO4, dehydrated and embedded for thin section electron microscopy. The use of the same fixative solution produced morphologically comparable precipitates from all three materials. The precipitates, especially after fixation in the presence of electrolyte, were composed of linear, unbranched filaments, frequently aggregated into bundles. The filaments were considered to be molecules of hyaluronic acid.