Effect of chlorpromazine in vitro on release of enzymes from lysosomes of the bovine retinal pigment epithelium

The effects of chlorpromazine on lysosomal enzymes and the release of enzymes from lysosomes of bovine retinal pigment epithelial cells were studied in vitro, using cathepsin D, arylsulfatase, and acid phosphatase as lysosomal marker enzymes. Chlorpromazine had little effect on the enzyme activity of cathepsin D and arylsulfatase and slightly decreased that of acid phosphatase. Chlorpromazine accelerated considerably the release of cathepsin D and arylsulfatase, but only minimally affected the release of acid phosphatase. The release of these enzymes from lysosomes depended on the dose of chlorpromazine.

Posterior and anterior permeability defects? Morphologic observations on streptozotocin-treated rats

Structural abnormalities of the blood-ocular barrier were examined in streptozotocin (STZ)-treated hyperglycemic rats, after 9 days, 6 months, and 10 months' duration of "diabetes," and in normoglycemic control animals using the horseradish peroxidase tracer technique combined with light and electron microscopy. The most frequent abnormalities consisted of small areas of diffuse dense staining by the tracer of (1) the retinal pigment epithelium and (2) the nonpigmented ciliary epithelium. Pigment epithelium abnormalities occurred occasionally in both groups of animals with approximately equal frequency and extent. Ciliary body abnormalities occurred also in both groups, but were frequent; statistically, the probability of these changes was not significantly different between the two groups. At the ora serrata, tracer escape was present through the retinal pigment epithelium into subretinal space and retina. Retinal vascular leakage occurred rarely and may be related to tracer toxicity rather than hyperglycemia. Thus, using the HRP method, we cannot confirm the claim that sustained STZ-induced hyperglycemia causes breakdown of the blood-retinal barrier in the rat.

Adrenaline: occurrence in the bovine retina

Using high performance liquid chromatography (HPLC) and electrochemical detection, a substance corresponding to adrenaline was identified in crude perchloric acid extracts from bovine retina. The substance did not originate from exogenous contamination such as blood. Retinal tissues also contained phenylethanolamine-N-methyl-transferase (PNMT) activity and the retinal enzyme had a similar substrate specificity as purified bovine PNMT. The pigment epithelium/choroid complex also had PNMT activity and an analysis of extracts by HPLC revealed the presence of small amounts of adrenaline. The results suggest that adrenaline is of functional importance in the bovine retina.

Effect of photic injury on the retinal tissues

In order to study the tissue damages in photic injury of the retina, the macula and posterior pole of the rhesus monkey were exposed to the light of an indirect ophthalmoscope. During the acute phase of the injury, disruption of the blood-retinal barrier appeared to be an early and sensitive indicator of retinal pigment epithelial damage and cyclic-GMP-phosphodiesterase of the photoreceptor lamella was inactivated. These lesions were followed for 2 to 5 years. Focal chronic decompensation of the blood-retinal barrier and subretinal pigment epithelial neovascularization were noted in the chronic degenerative phase of this photic maculopathy. A possible protective role of ascorbic acid in mild photic injury was proposed.

The enzymatic cleavage of rhodopsin by the retinal pigment epithelium. II. The carbohydrate composition of the glycopeptide cleavage product

The carbohydrate groups present in the glycopeptide cleaved from purified [3H]-GlcNAc-rhodopsin by an enzyme from the retinal pigment epithelium were analyzed in terms of the size of the oligosaccharide chains, the sequence of the sugars and their anomeric linkages. These analyses were performed also on intact rhodopsin and an enzyme control. The oligosaccharides were cleaved from the peptide by means of hydrazinolysis. After reduction with NaB3H4, the oligosaccharides, purified by paper electrophoretic and paper chromatographic means, were digested sequentially with exoglycosidases, and the resultant digestion products examined by high-resolution gel filtration on Bio-Gel P-4 (-400). The size, sequence and anomeric configuration of the constituents of the oligosaccharides present in the glycopeptide were essentially identical to those present in intact purified rhodopsin, indicating the retention by the glycopeptide of the sugar chains of the intact molecule.

Effect of temperature and pH on release of enzymes from lysosomes of the bovine retinal pigment epithelium in vitro

The effects of buffer concentrations, pH, and temperatures on the release of enzymes from lysosomes of the bovine retinal pigment epithelium were studied in vitro. Cathepsin D, arylsulfatase, and acid phosphatase were used as lysosomal marker enzymes. Elevation of temperature caused a marked increase in the release of cathepsin D and arylsulfatase from lysosomes, but little changes in the release of acid phosphatase. Acidic conditions accelerated the release of arylsulfatase and acid phosphatase. Different buffer concentrations had little effect on the release of these enzymes from lysosomes.

The enzymatic cleavage of rhodopsin by the retinal pigment epithelium. I. Enzyme preparation, properties and kinetics: characterization of the glycopeptide product

An enzyme system has been detected in the bovine retinal pigmented epithelium (RPE) which carries out the degradation of rhodopsin. The substrate for these studies was bovine rhodopsin labeled by in vitro techniques with [3H]-glucosamine or [3H]-mannose, the former being the derivative most extensively examined. Labeled rhodopsin was purified by adsorption and affinity chromatography followed by preparative isoelectric focusing. Cell-free preparations from bovine RPE cleaved rhodopsin to a single glycopeptide. The pH optimum for the reaction was about 3.5. The apparent Km for rhodopsin was about 5 microns. Rhodopsin was cleaved about 55% under saturating conditions, the limited extent of reaction due primarily to its partial inactivation for use as a substrate during the course of the reaction. Inhibition by cleavage products was not observed. Among several tissues which were examined, the RPE was the most active in rhodopsin-cleaving activity. Although stable as a crude extract, the activity of the rhodopsin-cleaving enzyme, as well as the bovine serum albumin (BSA)-cleaving enzyme (cathepsin-D) were rapidly lost upon purification by DEAE-Sephacel and pepstatin-Sepharose. Differences in relative specific activity among tissues as well as differential patterns of purification suggest that the rhodopsin-cleaving enzyme and the BSA-cleaving enzyme of the RPE may not be the same. Using N-retinylopsin as a substrate for the rhodopsin-cleaving enzyme, it was shown that the regions of the cleavage products containing vitamin A were not associated with the glycopeptide. Some of the properties of the product were examined. Its response to ion exchange resins, susceptibility to further cleavage by pronase, amino acid analysis, solubility properties, isoelectric point, and binding by concanavalin A (conA)-Sepharose, were consistent with the product being described as an acidic glycopeptide. The glycopeptide was reactive with the antibody prepared against bovine rhodopsin, and retained the full antigenicity of the intact molecule. This enzyme system may be one of the means whereby the RPE participates in maintaining the physiological concentration of rhodopsin which is synthesized in the retina and catabolized in the RPE.

The relative proportions of lysosomal enzyme activities in bovine retinal pigment epithelium

The lysosome fractions from bovine retina, liver and retinal pigment epithelium were isolated by subcellular fractionation and compared with regard to the relative proportions of several hydrolytic enzyme activities. It was found that the lysosome fraction of the retinal pigment epithelium is more than three times as active as the lysosome fractions from other tissues in degrading the rhodopsin of photoreceptor (rod) cell outer segments. This proteolytic activity is attributable to a cathepsin D-like proteinase, and the possible biochemical bases for its increased activity in the pigment epithelium are discussed, including interaction with phospholipase A. It is suggested that the lysosomes of the retinal pigment epithelium are specialized in their content of hydrolytic enzymes for the degradation of photoreceptor cell outer segments.

Tissue culture of cat retinal pigment epithelium

To culture retinal pigment epithelial (RPE) cells from normal cats, the cells were enzymatically dissociated from the eyecup and grown in either Ham's F-10 Nutrient Mixture or Eagle's Minimum Essential Media supplemented with 20% fetal calf serum. Cultures reached confluency between 6 and 10 days and contained monolayers of polygonally shaped cells. Light and electron microscopy demonstrated that most of the normal morphological characteristics of cat RPE cells in vivo were maintained in vitro; these included apical microvilli, apicolateral junctional specializations, basal infoldings and intracellular organelles. Pigment granules appeared to be diluted by cell division. No evidence of a basal membrane formation was seen; however, a fine granular or fibrillar extracellular matrix was observed in some cultures and was located between the culture plate surface and the basal surface of the RPE. Primary cultures were viable for up to 145 days. The activities of two lysosomal hydrolases (arylsulfatase A and arylsulfatase B) involved in the metabolism of sulfatide and dermatan sulfate were measured in confluent cultures. Mean arylsulfatase A activity was 1297 nmol nitrocatechol/mg protein/hr and arylsulfatase B activity was 553 nmol nitrocatechol/mg protein/hr. These activities were approximately 5 to 10-fold higher than present in cat peripheral leukocytes and skin fibroblasts in vitro. This in vitro system will facilitate studies on normal function and in conditions where the RPE has been compromised by inherited diseases (i.e. gyrate atrophy, mucopolysaccharidosis I and VI).

Permeability of the neonatal rat choriocapillaris to hemeproteins and ferritin

The permeability of the endothelium of the capillaries of the rat choriocapillaris to circulating macromolecules was examined during the first post-natal week of development using hemeproteins of different molecular dimensions and ferritin. At this stage of development capillaries and photoreceptor cells in the neural retina are not fully formed, but the choriocapillaris has an adult-like morphology. Thus, through these differences in neural and vascular architectures the possible functional relationships between the retina and choriocapillaris can be explored. High levels of horseradish peroxidase [Einstein-Stokes radius (ESR) 3 nm] activity were localized in Bruch's membrane within 2 minutes after intravenous tracer injection. In contrast, scant levels of hemoglobin (ESR, 3.2 nm) and no catalase (ESR, 5.2 nm) activity were observed here at 75 and 90 minutes, respectively. Only a few ferritin particles (ESR, 6.1 nm) crossed the choriocapillary endothelium after a 90-minute circulation. The results demonstrate that in the neonatal rat the choriocapillaris has the same restrictive properties as have been described for the adult eye (Pino and Essner, 1980, 1981), even in the absence of retinal capillaries and functional photoreceptor cells.

Mercapturic acid pathway enzymes in bovine ocular lens, cornea, retina and retinal pigmented epithelium

Analogous to the liver, ocular tissues contain large concentrations of glutathione and are exposed to potentially damaging chemical compounds. Since glutathione has been shown to have a detoxification function, via mercapturic acid production in the liver, we investigated whether glutathione has a similar function in ocular tissues. We have demonstrated the presence of all of the enzymes involved in the mercapturic acid pathway i.e. glutathione S-transferase, gamma-glutamyl transpeptidase, cysteinylglycinase, and N-acetyl transferase, in the ocular tissues of bovine lens, cornea, retina, and retinal pigmented epithelium. Therefore glutathione may have another function in ocular tissues, that of the detoxification of xenobiotics.

Lysosomal enzymes in the interphotoreceptor matrix: acid protease

Interphotoreceptor matrix (IPM), washed from the retina and retinal pigment epithelium (PE) of adult bovine eyes, was assayed for acid protease. Considerable enzyme activity was observed in the IPM--close to one-tenth of the total acid protease of the entire retina-IPM-PE functional unit. The specific activity was much higher in that part of the matrix near the PE. Based on the finding of an acid hydrolase in the IPM, the possibility is discussed that PE cells may secrete lysosomal enzymes and that the process of shed-disc digestion may begin in the IPM, prior to phagocytosis by the PE.

ATPase activities of human retina and pigment epithelium-choroid

The Mg2+-, the Na+-K+-, and the HCO3--stimulated ATPase activities have been measured in the retina and pigment epithelium of postmortem human donor eyes. Activities were measured between 24 and 72 hr after death, following storage of the eyes in moistened chambers kept in a refrigerator. There appeared to be no significant differences in the ATPase activities between the 24 and 72 hr tissues. The human retina demonstrated both Mg2+- and Na+-K+-stimulated ATPase activity, but no HCO3+-stimulated ATPase activity, but not HCO3+-stimulated ATPase activity. The Na+-K+ ATPase activity was 1.54 mumol Pi/hr/mg protein, which amounted to 37% of the total ATP hydrolysis of the retina. The pigment epithelium-choroid showed significant Mg2+-, Na+-K+-, and HCO3--stimulated ATPase activities, with the stimulation caused by HCO3- about 25% greater than the effect due to Na+-K+, 0.64 vs. 0.51 mumol Pi/hr/mg protein. These findings in human retina and pigment epithelium-choroid show that certain metabolic processes continue to operate for several days after death.

Carbonic anhydrase distribution in the rabbit eye by light and electron microscopy

The distribution of carbonic anhydrase (CA) in the rabbit eye was studied by light and electron microscopy according to the histochemical method of Hansson. In the cornea, CA staining was found in the cytoplasm of the endothelium. The filtering tissue in the chamber angle did not stain. The pigmented epithelium of the iris and the non-pigmented epithelium of the ciliary body showed intense staining distinctly located at lateral and apical cell membranes, without clearcut regional differences. In the Müller cells of the retina cytoplasmic staining was found. The dilatator muscle of the iris, the pigmented epithelium of the ciliary body, and the pigment epithelium of the retina showed similar and intense staining: cytoplasmic, mitochondrial, and at the cell membranes. The similarity of CA staining in these areas suggests similarity in function, possibly as transport processes important for the nutrition of the overlying cells. However, the role of CA in the various locations remains speculative, except in the corneal endothelium and the prelenticular ciliary processes, where the enzyme is evidently concerned with transport of salt and water.

Gamma-glutamyl transpeptidase in the pigment cells of rhesus eyes

We demonstrated that gamma-glutamyl transpeptidase, one of the enzymes of the gamma-glutamyl cycle, is present in the melanocytes of the eyes of rhesus macaques. Enzyme activity was detected in active melaninsynthesizing melanocytes of the iris stoma and in fetal and neonatal retinal pigment epithelium. It was not detected in adults retinal pigment epithelium or choroidal melanocytes, which are ontogenetically more advanced in development and have little melanogenic activity. Our data show that gamma-glutamyl transpeptidase activity correlates well with growth, early differentiation, and active melanogenesis, and support the hypothesis that in addition to tyrosinase, a second enzyme, such as gamma-glutamyl transpeptidase, takes part in the melanin and pheomelanin metabolic pathways.

The distribution of peroxide regulating enzymes in the canine eye

The retina and rod outer segments (ROS), rich in unsaturated lipids, are highly susceptible to autoxidation via free radical mechanisms. In the canine eye, four enzymes, i.e.; p-phenylenediamine (PPD) peroxidase, glutathione peroxidases, catalase and superoxide dismutase which are involved in the production or degradation of peroxides, were measured. All enzymes were present in the retina, ciliary body and iris, but differed in concentration. Superoxide dismutase showed high activity in the ROS. In the retinal pigment epithelium (RPE) a peroxidase utilizing PPD as cosubstrate and superoxide dismutase were both present. The former enzyme was found equally distributed between soluble and insoluble forms. A pigment granule fraction from the RPE only contained PPD-peroxidase. The compartmentalization of peroxide regulating enzymes in the eye is striking. Whereas the retina seems well protected against superoxide free radicals and hydrogen peroxide by virtue of superoxide dismutase, peroxidases and catalase activities, the ROS are only protected by superoxide dismutase. Therefore, after phagocytosis of the ROS, any peroxidized lipids, organic peroxides, or unconverted superoxide radicals contained within the ROS, must be detoxified by a specific RPE peroxidase and superoxide dismutase. Hydrogen peroxide or other peroxidized compounds apparently are not degraded by glutathione peroxidases or catalase, since these enzymes were not measurable in our RPE preparations. The role of antioxidative enzymes in the eye, which retard peroxide and free radical information, appears to be specific and regional.

Ornithine ketoacid aminotransferase in the bovine eye

Ornithine ketoacid aminotransferase in bovine ocular tissues was studied biochemically. The retinal pigment epithelium, ciliary body, iris, and neuroretina showed high specific activity. The cornea and choroid revealed a lower activity. Aqueous humor, lens, vitreous body, and sclera showed no activity. The pH optima of the enzyme in the retinal pigment epithelium and ciliary body were near 8.0.

[Glutathione peroxidase activity of frog eye pigment epithelium]

A highly active glutathione peroxidase (80% of which is localized in the water-soluble fraction) was detected in frog eye pigment epithelium tissue. It was shown that more than 75% of the glutathione peroxidase activity of the pigment epithelium tissue is bound to the Se-dependent enzyme. The Km values for glutathione and tret-butyl hydroperoxide were determined. It was found that Se, being a constituent of the melanoprotein granules, is not coupled to glutathione peroxidase.

Enzymatic esterification of vitamin A in the pigment epithelium of bovine retina

The kinetic properties and subcellular distribution of an esterifying enzyme in the pigment epithelium of bovine retina have been studied using both [1-3H]retinol and [3H]retinol bound to cellular retinol-binding protein as substrates. The most active esterifying fraction in pigment epithelial cell preparations was the microsomes, but the lysosome plus mitochondria fraction also showed some activity, probably due to endoplasmic reticulum present as an impurity. The microsomal enzyme showed optimum activity at pH 7.5, and the reaction was linear up to 30 microgram protein and for the first 10-15 min. The apparent Km values were 16.6 . 10(-6) and 5.5 . 10(-6) M for [3H]retinol and bound [3H]retinol, respectively. This is the first time that retinol bound to cellular retinol-binding protein has been shown to undergo metabolic transformation. The microsomal esterifying activity was destroyed by boiling for 1 min, or after freezing for 2 months. No clear requirement for ATP, CoA or fatty acid could be demonstrated. Of all the other tissues examined under the same experimental conditions as those used for the pigment epithelium, only intestine showed measurable activity. With larger amounts of tissue protein and longer incubation periods, activity was also detectable in microsomes of liver, testis and retina.

Ornithine aminotransferase in chick embryo tissues

Ornithine aminotransferase (E. C. 2.6.1.13) deficiency has been found to be associated with congenital atrophy of the choroid and retina of man. A deficiency in this enzyme could be associated in a causal fashion with atrophy, or it could be a coincidental association. To challenge the hypothesis that ornithine aminotransferase activity is required directly or indirectly for maintaining the eye in a functional state, it was of interest to determine the level of activity of this enzyme in normal eye tissue. We report here that the level of ornithine aminotransferase activity in pigment epithelium of chicken is 11 times that found in liver. The level of enzyme activity in retina is 80% of that found in liver. The level of enzyme present in embryonic pigment epithelium is essentially unchanged between the eighth and eighteenth day of incubation. These observations suggest strongly that ornithine aminotransferase activity is involved in maintaining the structure or function of the eye.

Fine structural demonstration of tyrosinase activity in the retinal pigment epithelium of normal and PTU-treated chick embryos

The effect of phenylthiourea (PTU) on the retinal pigment epithelium of chick embryo was studied by using electron microscopy and electron-microscopic histochemistry. In the retinal pigment epithelium of PTU-treated, 10-day-old chick embryo, there is an abundance of premelanosomes and relative increases in the smooth endoplasmic reticulum (ER), and in the smooth-surfaced anastomosing tubular channels. Reaction products resulting from electron-microscopic histochemistry are first observed in some cisternae of the distal or active face of the Golgi apparatus and occasionally in small vesicles in the 5-day-old embryo, and these reactions become more intense with time. PTU treatment blocks melanin synthesis in the premelanosomes of 10-day-old chick embryo. Electron-microscopic histochemistry is completely inhibited by PTU treatment. Removal of PTU allows a weak positive reaction to histochemistry in some elements of the Golgi apparatus and in some small vesicles.

An electron microscopic study of macrophages in rats with inherited retinal dystrophy

In retinas of rats (RCS) with inherited retinal dystrophy, cells interpreted as macrophages infiltrate the outer nuclear layer and subsequently appear in the interphotoreceptor space, where they accummulate during the course of the disease. The morphology and distribution of these cells and their relations to the pigment epithelial cells were investigated. Macrophages, regardless of their location, possessed morphological features that distinguished them from the pigment epithelial cells. Premelanosomes and melanosomes, typical of pigment epithelial cells, were never observed in macrophages. There was no evidence to indicate that, during the period studied, the pigment epithelial cells had become dedifferentiated or had migrated from Bruch's membrane. Macrophages, like pigment epithelial cells, phagocytized little or no outer segment material. The findings indicate that, at least during the interval studied, the cells that infiltrate the retina and interphotoreceptor space are macrophages rather than pigment epithelial cells.

Glycosidases of the retinal pigment epithelium

The pH optima and apparent Km and Vmax values were determined for nine glycosidases of the retinal pigment epithelium (RPE) of the calf. In terms of micromoles of substrate cleaved per milligram protein per hour, the following relative order of enzymatic activities was observed: beta-N-acetylglucosaminidase greater than alpha-glucosidase = beta-N-acetylgalactosaminidase greater than alpha-mannosidase greater than beta-galactosidase greater than beta-glucosidase greater than alpha-fucosidase greater than alpha-galactosidase greater than beta-glucuronidase. The pH optimum of each of these enzymes was in the acidic range (below pH 6). All these findings refer to enzymatic activities of bovine RPE preparations obtained by the brushing procedure of Glocklin and Potts and washing as described by Berman and Feeney. Thus they may relate to those activities associated with particulate components of the RPE cell and not to the more soluble glycosidases. The distribution of the glycosidases between the washes of the cells and the final pellet of bovine RPE cells was examined. The activities of 10 glycosidases in the RPE of the embryonic chick were also examined. Neither beta-mannosidase nor beta-fucosidase activities could be detected in washed bovine RPE cells, although beta-mannosidase was detected in RPE of the embryonic chick. The presence of isoenzymes of beta-glucuronidase in bovine RPE was indicated. Specificity by beta-glucuronidase of bovine RPE for synthetic substrates was observed.

Studies on the retina and the pigment epithelium in hereditary canine ceroid lipofuscinosis, I. The distribution of enzymes in the whole retina and pigment epithelium

The massive accumulation of autofluorescent lipopigments, representative of autoxidation, is a key morphological feature in canine ceroid lipofuscinosis (CCL). In the eye peroxidase, catalase, and four acid hydrolases were compared with regard to aged and clinical condition in a series of English setters affected with CCL. In unaffected English setters "soluble" peroxidase increased in the RPE to adult levels at 2 yr of age. Affected dogs had higher RPE peroxidase activity earlier in life, which then decline with age. The soluble retinal peroxidase of both unaffected and CCL dogs increased steadily with age, but the latter group of dogs were much lower in activity. By 2 yr of age, RPE and retinal peroxidase values were only 25% and 47% of unaffected dog levels. Although the soluble enzyme of unaffected dogs exhibited a maturational profile, membrane-bound RPE peroxidase showed a hyperbolic curve reaching a maximum at 10 mo of age. By 2 yr of age, the "bound" enzyme in affected dogs was below unaffected levels in the RPE and retina. Three acid hydrolases were slightly increased in the RPE and retina of affected dogs. Acid lipase activity, however, was similar in both unaffected and CCL dogs. Catalase was not found in the RPE of either group of dogs. The catalase activity in the retina of both affected and unaffected dogs was at similar levels. Since catalase is not present in the RPE, the major defense against peroxidase accumulation and peroxide toxicity probably depends upon peroxidase. The present study indicates that a decrease in this key regulating enzyme may be related to the formation of lipopigments in the retina and RPE of dogs with CCL.

Studies on the retina and the pigment epithelium in hereditary canine ceroid lipofuscinosis. II. The subcellular distribution of lysosomal hydrolases and other enzymes

Observations on the progressive course of retinal degeneration in canine ceroid lipofuscinosis (CCL) showed dramatic changes in enzyme activity and subcellular compartmentation. Thus, in affected animals, a new particle containing high levels of hexosaminidase and galactosidase was found in fractions lighter than seen in controls. In the later stages of disease and in normal aging, a progressive increase in dense fractions with high titers of acid lipase and acid phosphatase was observed. Peroxidase was found predominantly in the heavier fractions (1.24 to 1.28 gm/ml) and was lower than normal in affected retina and RPE. These fractions were located above the pigment granule fraction. Changes of peroxidase activity in the pigment granules were age dependent in controls, but a decrease of similar magnitude occurred much earlier in affected dogs. The accumulation of large numbers of dense bodies in the retina and RPE in CCL may indicate an impairment of intracellular digestive mechanisms. The early and marked reduction of peroxidase activity in affected dogs is an important indicator for major changes in the biochemistry of the entire eye in this disease. Therefore the initial pathogenic event seems to be the inability of affected cells to cope with peroxidative damage at an early stage, followed by an exaggerated attempt by the cells to digest accumulating lipopigments.

Lipofuscin and melanin of human retinal pigment epithelium. Fluorescence, enzyme cytochemical, and ultrastructural studies

The life history of melanin and lipofuscin granules of human retinal pigment epithelium (RPE) was studied in 30 human eyes spanning nine decades of life. Autofluorescent granules in the cytoplasm of eye over 30 years of age were shown, ultrastructurally and through lipid solvent extraction, to be lipofuscin granules. Sparse small fluorescent granules in infant eyes were secondary lysosomes containing small droplets of lipid. Flourescent substances in RPE granules of eyes less than 50 years old were more readily extracted with lipid solvents than those in very old eyes (greater than 70). Lipfuscin granules were positive for acid phosphatase and aryl sulfatase activity. Fusions between primary lysosomes and lipofuscin granules were common in older eyes, suggesting that the over-all degradative process involves repeated injection of lysosomal enzymes, i.e., the initial fusion of lysosomes with phagosomes (phagocytized outer segment disks) is only one of several attempts to hydrolyze the membranous material. Some melanin granules showed hydrolytic enzyme reactions. By use of enzyme cytochemistry, fluorescence microscopy, and lipid extraction two types of melanin-containing complex granules were identified: melanin with a cortex of lipofuscin (melanolipofuscin) and melanin with a cortex of nonlipid, enzyme reactive material (melanolysosomes). These findings indicate that melanin commonly becomes incorporated into the lysosomal system of the RPE cell and suggests that it undergoes modification or degradation there. These studies indicate that a dynamic, complex interrelationship exists between the various components of the phagolysosomal system and the melanin granules in the RPE cytoplasm. Also, the observed variation from one human eye to another in the content and lipid extractability of RPE lipofuscin granules suggests that there may be differences in lipid composition of phagocytized photoreceptor disks and/or differences in the degradation of these lipids in the phagolysosomal system of the RPE cell.

Demonstration of tyrosinase in the adult bovine uveal tract and retinal pigment epithelium

Modern techniques offer an opportunity for a more complete evaluation of melanin production in the uvea and retinal pigment epithelium (RPE). By measuring the release of tritium from tritiated tyrosine in homogenized samples of adult bovine RPE as well as iris and choroid, tyrosinase activity could be demonstrated in both the uveal tract and the RPE. Phenylthiourea, a specific tyrosinase inhibitor, markedly decreased tyrosinase activity, whereas 3-iodo-tyrosine, a tyrosine hydroxylase inhibitor, had no effect. These techniques indicate tyrosinase activity in the uveal tract and the RPE of adult cattle. This is the first biochemical demonstration of tyrosinase in adult RPE.

The ultrastructure of the retina in adult metachromatic leukodystrophy

A 46-year-old woman afflicted with biochemically proven metachromatic leukodystrophy had only mild optic atrophy shortly before her death. Repeated earlier ophthalmoscopic examinations had not revealed any retinal abnormalities. Light microscopy of the retina showed strong acid phosphatase activity in both enlarged ganglionic cells and pigment epithelial cells. Demyelination of both optic nerves was not noted. Ultrastructurally, membranous lysosomal residual bodies were confined to ganglionic cells. We found lipofuscin material in pigment epithelial cells, but also within metachromatic leukodystrophy-specific residual bodies of ganglionic cells. The presence of lipofuscin represents the "wear-and-tear" phenomenon, possibly enhanced by the metachromatic leukodystrophy.

Morphology of the rectinal pigment epithelium in the vitamin A deficient rat

Ultrastructural changes in the retinal pigment epithelium (RPE) and adjacent photoreceptor cells have been followed in the Wistar rat during the course of long-term vitamin A deficiency. Of particular interest has been the discovery of unusual concentric aggregates within the photoreceptor outer segments and the inner cytoplasm of the RPE. The aggregates were present throughout the course of the retinal degeneration induced by vitamin A deficiency and could be identified in the RPE either by themselves in the apical cytoplasm or within phagolysosomes. It is postulated that the concentric aggregates result initially from abnormal formation or condensation of outer segment membranes and are then slowly degraded by lysosomal action in the RPE cytoplasm. In addition, acid phosphatase activity and typical phagosomes (shed outer segment packets) have been demonstrated in the cytoplasm of the RPE of the vitamin A deficient rats. The latter findings indicate that, at least to some extent, the normal phagocytic and lytic processes of the RPE are retained in this nutritional disorder.

Localization of lysosomal enzymes in retinal pigment epithelium of rats with inherited retinal dystrophy

Four acid hydrolase activities are demonstrable by light microscopy in pigment epithelial cell lysosomes of rats (Royal College of Surgeons--RCS) with inherited retinal dystrophy and in control (Fischer) rats. The enzymes include acid phosphatase, aryl sulfatase, N-acetyl-beta-glucosaminidase, and esterase activities. No marked differences are observed in distribution or staining intensity of lysosomes in the two strains of rat. Acid hydrolase activities are not localized in sites other than lysosomes. Acid phosphatase and aryl sulfatase activities are also demonstrable by electron microscopy. In both strains, acid phosphatase reaction product is localized to various forms of lysosomes in pigment epithelial cells. A diffuse precipitate, considered to be nonspecific in origin, is seen in the cytoplasm, apical processes, outer segments (control), and outer segment debris (RCS). The precipitate is probably due to adsorption of lead from the incubation medium or of lead phosphate that diffuses from heavy accumulations in nearby lysosomes. Aryl sulfatase reaction product, in contrast to acid phosphatase, is localized to far fewer lysosomes and there is virtually no nonspecific precipitate. The findings indicate that lysosomes of RCS pigment epithelial cells possess several cytochemically demonstrable acid hydrolase activities. There is no evidence for the localization of acid phosphatase (or aryl sulfatase) activities in sites other than lysosomes.

An enzyme histochemical analysis of human subretinal fluid

During rhegmatogenous retinal detachment, two major phagocytic cell populations can be identified in the subretinal fluid. Routine light and electron microscopic studies may be inadequate to assess quantitatively the free-floating retinal pigment epithelial cells and the macrophagic retinal pigment-laden cells. Enzyme histochemical staining permits a simple, rapid, reproducible method of identifying each cell type. This cytologic biochemical differentiation is an important tool for reexamination of the theories associated with subretinal fluid cell activity.

Trysinase positive oculocutaneous albinism in the goldfish, Carassius auratus l., and ultrastructural and biochemical study of the eye

Ultrastructural studies, and cytochemical and biochemical determinations of tyrosinase activity were conducted on the pigment epithelium of albino and xanthic goldfish eyes. In eyes of xanthic goldfish, two types of melanosomes are present, spherical and elongated. Melanized melanosomes are absent in the eyes of the albino goldfish, but elongated lamellar premelanosomes are observed. Internal vesicles are present in both melanosome types in the pigment epithelium of the xanthic goldfish but are absent in premelanosomes of the albino. There are also differences in the distribution of lipid droplets, smooth endoplasmic reticulum and Golgi complexes with the latter two being more abundant in the albino. Tyrosinase was not identified cytochemically; however, the enzyme was demonstrated biochemically in the pigment epithelia of both albino and xanthic goldfish. The enzyme is associated with the particulate and soluble fractions fo both types of eyes. Particulate albino tyrosinase may be solubilized by triton X-100 treatment. Tyrosinase inhibitors are present in the particulate fractions of both albino and xanthic goldfish eyes. Thus, in the goldfish, ocular albinism appears to be a multiple defect at the molecular and ultrastructural levels.