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Biomedical subjects

R N Frank

Publications and source records attributed to R N Frank.

At least 55 records · Page 3Linked to original sources
PubMed1988

ATP causes retinal pericytes to contract in vitro.

We evaluated the contractility of bovine retinal microvascular pericytes in culture by permeabilizing the cells with 0.1% Triton X-100 and measuring their response to MgATP. Sequential photographs of the cells were taken over 20 min and their surface areas were measured. Our study directly demonstrates that pericytes are contractile cells, which respond to MgATP in a dose-dependent fashion over a relatively short time course (minutes). Pericytes did not contract in response to GTP, pyrophosphate or beta, gamma-methylene ATP. Immunofluorescence study showed the presence of muscle actin in Triton X-100-treated cells before and after contraction, indicating preservation of this cytoskeletal protein even after treatment with the detergent. Similar experiments on human umbilical vein endothelial cells, bovine lens epithelial cells and human retinal pigment epithelial cells showed that these cells were significantly less contractile than retinal pericytes. That pericytes show substantial contraction over a short time course indicates that these cells may play a major role in regulating blood flow in the microcirculation.

Actins↗
PubMed1987

Cerebral cortical capillary basement membrane thickening in galactosaemic rats.

Wistar-Kyoto rats fed a diet containing 30% by weight galactose for 15-21 months developed significant thickening of the endothelial basement membranes of capillaries from the frontal cortex of the cerebrum, by comparison with cerebral capillary basement membranes from animals on a standard diet (p less than 0.001), or animals receiving a diet containing 30% galactose together with 250 mg/kg diet of the aldose reductase inhibitor, Sorbinil (0.001 less than p less than 0.01). The effect was similar to that which we have reported previously in the retinal capillaries of these animals. Spontaneously hypertensive rats on the high-galactose diet showed modest cerebral capillary basement membrane thickening (0.02 less than p less than 0.05) only for one of the measurement protocols utilised, and the process was not prevented by Sorbinil. Biochemical assays of retina, cerebral cortex, and blood serum from Wistar-Kyoto and spontaneously hypertensive rats maintained on the Sorbinil regimen showed that the drug did cross the blood-retinal and blood-brain barriers. Similar to our previous study on the retinal capillaries, we observed no degeneration of pericyte or endothelial cell cytoplasm, and no alteration in the pericyte/endothelial cell nuclear ratio in the cerebral capillaries of galactosaemic animals, by comparison with controls. Based on immunocytochemical studies in the human retina, it has been claimed that aldose reductase is present in capillary pericytes but absent in the endothelial cells. However, we observe a considerably smaller pericyte/endothelial cell nuclear ratio in the capillaries of the cerebral cortex of the rat, by comparison with those of the retina.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Pericyte coverage is greater in the retinal than in the cerebral capillaries of the rat.

Using electron microscopic morphometry, we demonstrate here that, in the albino rat, the pericytes of the retinal microcirculation over the capillary circumference much more extensively than in five widely separate regions of cerebral cortex. The ratio of pericyte plasma membrane length in contact with the vascular circumference, to the outer circumference of the endothelial cell tube, was 0.41 +/- 0.02 (SEM) for the retinal microvessels, and ranged from 0.22 +/- 0.02 to 0.30 +/- 0.03 for the five regions of cerebral cortex. The values of this ratio for the retina differed significantly from those for the various cortical regions. Differences of comparable magnitude were obtained between ratios of pericyte to endothelial cell areas in retina and cerebral cortex. The substantial quantitative difference in pericyte coverage of the microvessel circumference between the retinal and cerebral microcirculations may have important implications for normal and pathological microcirculatory dynamics in these two organs.

Animals↗
PubMed1986

Retinal dystrophy: development retarded by galactose feeding in spontaneously hypertensive rats.

Retinal photoreceptor cell dystrophies have been widely observed in humans and in animals, but pathogenetic mechanisms are known in only a few such disorders, and successful therapeutic intervention has been reported in fewer still. Spontaneously hypertensive albino rats develop a retinal photoreceptor cell dystrophy with onset late in the first year or early in the second year of life. Between 60 and 70 percent of the animals are affected. A substantial reduction in the prevalence and severity of the dystrophy occurred in such animals whose diet contained 30 percent (by weight) D-galactose. Neither an inhibitor of the enzyme aldose reductase, present in the diet, nor diabetes mellitus, induced by streptozotocin, had any statistically significant influence on the dystrophy. Ambient light and systolic blood pressure levels also did not seem to influence the course of the disorder. The mechanism by which galactose exerts its effect is unknown, but a mutant enzyme with an elevated Michaelis constant (Km) for galactose is plausible.

Age Factors↗
PubMed1986

Collagens of the retinal microvascular basement membrane and of retinal microvascular cells in vitro.

We have analysed the collagens present in vascular basement membranes isolated from bovine retinal and cerebral microvessels and bovine renal glomeruli, and from the non-vascular basement membrane of bovine lens capsule. These are compared with the collagens produced by cultured bovine retinal microvascular pericytes and lens epithelial cells, and by canine retinal microvascular endothelial cells, in vitro. Biochemical and immunocytochemical analyses indicate that all of the vascular basement membrane preparations have an identical collagenous composition, consisting of the same polypeptides present in lens capsule (primarily type IV collagen), together with other polypeptides that are identified as type I, and a small amount of type III collagen. Identification of the latter is based on two-dimensional gel electrophoresis in the presence and absence of a reducing agent. Immunocytochemical studies, however, demonstrate type I, type IV and some type V collagen in the basement membranes of the isolated microvessels. The cultured microvascular cells produce predominantly type I collagen molecules, but they also produce other collagen peptides that appear to be type IV, and, at least in some experiments, small amounts of type III collagen. The biochemical identification of collagens type I and IV is confirmed by immunocytochemistry. However, results with anti-type I collagen and procollagen antibodies in cultured pericytes vary with antibodies from different sources. The quantities of the type IV peptides produced by the cultured cells also vary in different experiments.

Amino Acids↗
PubMed1986

Aldose reductase activity and basement membrane thickening.

Rats fed a high-galactose diet develop marked thickening of their retinal capillary basement membranes. The effect is prevented if the animals also receive the aldose reductase inhibitor sorbinil. The effect does not appear to be due to aldose reductase itself, since immunoreactive aldose reductase has not been found in the retinal microvasculature of the rat but rather to a related enzyme with similar substrate specificity. The detailed biochemical mechanism for basement membrane thickening is obscure, involving an alteration of the extracellular matrix, where aldose reductase and similar enzymes have not been described; osmotic damage to the microvascular cells, such as has been described following aldose reductase-induced sugar alcohol accumulation in lens epithelial cells, is not apparent in diabetic or galactosemic animals. It is possible that concentrations of intracellular sugar alcohols that do not substantially change the osmolarity of the cell cytosol alter intracellular enzyme activities. This, in turn, could affect the biosynthesis of extracellular matrix macromolecules, as suggested, for example, by the hypothesis of Rohrbach et al, based on studies of a basement membrane-producing tumor implanted in diabetic mice, which proposes that the hyperglycemia of diabetes mellitus causes a reduced synthesis of the heparan sulfate BM-1 proteoglycan with a subsequent overproduction of type IV collagen. This and other hypotheses of basement membrane thickening can be tested in diabetic or galactosemic rats, some of which receive aldose reductase inhibitors, or in retinal microvascular pericytes and endothelial cells grown in culture.

Aldehyde Reductase↗
PubMed1986

Diabetic retinopathy: current concepts of evaluation and treatment.

Diabetic retinopathy is a common, and potentially blinding or visually disabling complication of diabetes. Nearly all diabetic subjects will have some degree of retinopathy after 20 years of diabetes, and 50% of those with insulin dependent diabetes will have proliferative retinopathy after 15 years. Macular oedema frequently produces central vision loss and legal blindness, most commonly in non-insulin dependent diabetics. In recent years, several therapeutic modalities have been demonstrated to be effective on the basis of large-scale randomized, controlled clinical trials. These include panretinal photocoagulation (PRP), using the argon laser or xenon arc, for proliferative retinopathy, and focal photocoagulation for macular oedema. Vitrectomy surgery is effective for diabetic vitreous haemorrhage and traction retinal detachment, producing improved vision in most patients, but only a relatively small percentage of patients so treated recover good visual acuity (greater than or equal to 6/12). Other therapeutic modalities, such as hypophysectomy for severe retinopathy, remain controversial, while still others, such as rigorous blood glucose control and aldose reductase inhibitors, are currently under investigation. The primary care physician who deals with diabetic patients should be familiar with the lesions of diabetic retinopathy and with current therapeutic modalities. He should perform an examination of the posterior retina with the direct ophthalmoscope on each diabetic patient at each visit, and should institute prompt referral to an ophthalmologist at the first sign of change. Periodic examination of all diabetic patients by an ophthalmologist should be conducted at the intervals recommended in the previous section. Definitive evaluation and treatment of diabetic retinopathy should be carried out by the ophthalmologist.

Adult↗
PubMed1986

Presumed retinovitreal neovascularization in dystrophic retinas of spontaneously hypertensive rats.

The authors have observed abnormal blood vessels, strongly suggestive of neovascular proliferation, arising from the retinal circulation and extending through the inner limiting membrane of the retina into the vitreous in five spontaneously hypertensive (SHR) rats with severe retinal dystrophy. The animals in whom these presumptive retinovitreal new vessels occurred were all 15 mo of age or older. The new vessels frequently demonstrated thinned and, rarely, fenestrated endothelium, abnormal intracellular junctions, increased numbers of endocytic vesicles, bizarre appearing pericytes, and highly abnormal basement membranes, features that have been observed in retinovitreal new vessels in proliferative retinopathies in humans. Unlike such new vessels arising from the human retinal circulation, however, those that we observed in dystrophic rat retinas were usually surrounded by proliferating retinal pigment epithelial cells within the retinal substance. Unlike the vessels, the pigment epithelial cells did not break through the inner limiting membrane of the retina to enter the vitreous. The pigment epithelial cells that made contact with the internal limiting membrane of the retina demonstrated apical and basal plasma membrane specializations that are typical of these cells in their normal anatomical location, while pigment epithelial cells migrating in cords through the neural retina lacked such specializations. This animal model may be of great value in understanding the mechanisms of retinal neovascularization.

Animals↗
PubMed1986

In vitro production of glycosaminoglycans by retinal microvessel cells and lens epithelium.

Analysis of bovine lens capsules and retinal microvessel basement membranes by cellulose acetate electrophoresis, together with treatment by specific enzymes or by nitrous acid, reveals that heparan sulfate is the only demonstrable glycosaminoglycan (GAG), consistent with the observations of most other investigators on basement membrane preparations from several different tissues. When bovine retinal microvessel pericytes or endothelial cells or bovine lens epithelial cells are grown in culture in the presence of [35S]-sulfate or [3H]-glucosamine, however, both cellulose acetate electrophoresis and gel filtration chromatography reveal that the cultured pericytes synthesize primarily chondroitin sulfate, whereas the lens epithelial cells and microvascular endothelial cells produce a mixture of GAGs consisting of approximately 60% heparan sulfate and 40% chondroitin sulfate. The chondroitin sulfate chains have an Mr of 70,000, but the Mr of the heparan sulfate chains is 10,000, based on gel filtration chromatography on Sepharose CL-6B. Hence, cell culture conditions may produce phenotypic modulation of the biosynthetic capacities of these cells for GAGs. However, the difference between the in vitro and in vivo findings may in part be explained if many of the chondroitin sulfate GAGs synthesized in vitro are cell associated and are not incorporated into the basement membrane.

Animals↗
PubMed1986

Does the retinal pigment epithelium polarize the choriocapillaris?

Morphometric evaluation of choroidal capillaries from spontaneously hypertensive (SHR) rats with anatomically normal and severely dystrophic retinas reveals a marked polarization of endothelial fenestrations, endothelial cytoplasmic thickness, and endothelial cell nuclei. The mean density of fenestrations per unit endothelial length is greatest and the cytoplasmic thickness and number of nuclei is least in capillary sectors closest to the retinal pigment epithelium (RPE), with a statistically significant, continuous decrease in density of fenestrations and an increase in endothelial thickness and nuclear numbers in sectors progressively farther from the RPE. Abnormal capillaries derived from the retinal circulation and growing within the RPE also have fenestrations, but show no anatomic polarization. These results are consistent with the recently proposed hypothesis that a diffusible, trophic factor, produced by the RPE and secreted from its basal surface, modulates the structure of nearby vascular endothelial cells. However, the endothelial cells themselves probably also influence the structure of the RPE, since complex infoldings of the RPE plasma membrane, identical to those normally present in its basal surface, are also extensively present surrounding the abnormal intra-RPE capillaries.

Animals↗
PubMed1984

On the pathogenesis of diabetic retinopathy.

Recent investigations of retinal vascular cells in tissue culture, animal models, and diabetic human subjects suggest several potential pathogenetic mechanisms for diabetic retinopathy. These include the enzyme aldose reductase, which appears to be responsible for basement membrane thickening in galactosemic rats (since the lesion is prevented by an aldose reductase inhibitor), and a picture, in galactosemic dogs, that closely resembles early, background diabetic retinopathy; insulin, which stimulates, and elevated glucose levels, which inhibit in vitro proliferation of retinal pericytes. Various hormones, including the sex hormone, the insulin-like growth factors and, perhaps independently, growth hormones, may influence the later stages of diabetic retinopathy. Chronic hyperglycemia appears to be the primary pathogenetic agent in diabetic retinopathy as well as in other complications of diabetes, but the different rates of onset and progression of these complications suggest that glucose acts through different biochemical pathways that are probably under different genetic control. Finally, the locus of the primary biochemical lesion in diabetic retinopathy may reside in the neuronal or glial cells of the retina, with the retinal blood vessels only secondarily involved.

Aldehyde Reductase↗
PubMed1983

Galactitol accumulation by glucose-6-phosphate deficient fibroblasts: a cellular model for resistance to the complications of diabetes mellitus.

When incubated in high galactose media, fibroblasts from individuals with the severe (Mediterranean) variety of glucose-6-phosphate dehydrogenase (G6PD) deficiency accumulate significantly less galactitol than do fibroblasts from matched control subjects. The effect is not observed in fibroblasts from black subjects with the more common, and milder, A- variant of G6PD deficiency. Since aldose reductase and sorbitol dehydrogenase activities in experimental and control fibroblasts are identical, the effect is most likely due to the substantial reduction in NADPH levels in severely G6PD-deficient cells. Sorbitol does not accumulate either in control or in G6PD deficient fibroblasts incubated in high glucose medium, most likely because of the action of sorbitol dehydrogenase, and the presence of a carrier-mediated glucose transport system in the cell membrane which limits the concentration of glucose that can accumulate in these cells.

Adolescent↗
PubMed1983

Correlates of delayed motor nerve conduction and retinopathy in juvenile-onset diabetes mellitus.

Using a protocol designed to eliminate observer bias, we studied the relationship of duration of diabetes, age, blood glucose control, and the presence of retinopathy to motor nerve conduction velocity in patients with juvenile-onset diabetes of short duration. Conduction velocities for both the ulnar and peroneal nerves were significantly slower in the diabetic subjects than in the controls. Duration of diabetes, age, and diabetes control each had significant and independent effects on the prevalence of delayed conduction. Delayed conduction was present in more than 20% of those with diabetes of less than five years' duration, whereas retinopathy was present in none of our subjects with diabetes of the same duration. Moreover, although the presence of retinopathy was closely correlated with the presence of delayed conduction velocity, a number of diabetic subjects had one abnormality but not the other. We believe that delayed nerve conduction and retinopathy in diabetic patients are caused by multifactorial mechanisms that share a common relationship to duration, age, and degree of hyperglycemia, but which differ in at least some fundamental aspects.

Adolescent↗
PubMed1983

Aldose reductase activity in retinal and cerebral microvessels and cultured vascular cells.

Isolated microvessels (primarily capillaries) from bovine retina and cerebral cortex, as well as cultured bovine retinal capillary pericytes and porcine and canine retinal capillary endothelial cells contain apparent aldose reductase activity. This conclusion is based on the ability of these cultured cells and vessel fragments to reduce DL-glyceraldehyde in preference to D-glucuronate at low (0.1 mM) substrate concentrations, in the presence of NADPH, and in the accumulation of high levels of sorbitol or galactitol when retinal pericytes and endothelial cells are cultured in media enriched in glucose or galactose. The quantitative similarities of these activities in bovine retinal and cerebral microvessels, as well as the quantitatively similar ability of these two sets of microvessels to oxidize 14C-labeled glucose with the label either in the C-1 or the C-6 position, suggests that aldose reductase may not be a major causal factor in diabetic retinopathy. This conclusion is suggested because, while these metabolic activities are similar in bovine retinal and cerebral microvessels, only the retinal microvasculature suffers major anatomic and functional damage in diabetes. This conclusion must be viewed with caution, however, because other metabolic pathways that we have not investigated may be altered by an excess of sugar alcohols, and be present in differing activities in retinal and cerebral microvessels; species differences may exist; and similar experiments have not been conducted using human microvessels.

Aldehyde Reductase↗
PubMed1983

Galactose-induced retinal capillary basement membrane thickening: prevention by Sorbinil.

Normotensive and spontaneously hypertensive rats fed a 30% galactose diet until 15-21 months of age developed significant (P less than 0.05) retinal capillary basement membrane thickening, compared with animals fed a standard test diet. Animals on the high galactose diet containing 250 mg/kg of the aldose reductase inhibitor, Sorbinil, did not develop basement membrane thickening. No cytologic abnormalities of pericytes or endothelial cells were noted, and pericyte:endothelial cell nuclear ratios did not differ in the various experimental groups. This model reproduces a characteristic lesion of diabetes mellitus in non-diabetic animals, and should facilitate study of the biochemical mechanisms of basement membrane thickening.

Animals↗
PubMed1982

Ocular complications.

Ocular complications of diabetes in humans are reviewed briefly, and experimental models available for study of the complications are described. Potentially suitable models include not only diabetic animals, but also nondiabetic animals in which analogous lesions have been demonstrated. Many abnormalities of the lens, cornea, iris, and retina comparable to those of diabetes in humans may be observed in diabetic animals, although all abnormalities are not necessarily observed in every species. Retinal changes, in particular, may occur in diabetic animals of several species, but only in large animals (dogs, primates) have saccular capillary aneurysms been reproduced consistently, together with other retinal changes typical of diabetes in humans. A few examples of the uses of animal models are offered, and attention is called to a lack of animal models of proliferative diabetic retinopathy and of rubeosis iridis.

Animals↗
PubMed1982

Retinopathy in juvenile-onset type I diabetes of short duration.

We evaluated the prevalence and severity of diabetic retinopathy in 173 juvenile-onset, type I diabetic subjects and 78 nondiabetic controls of similar age, race, and sex distribution by stereoscopic fundus photography and fluorescein angiography, performed by a standardized protocol and evaluated by five expert, masked observers. The overall prevalence of retinopathy was 18% in the diabetic group and 0% in the controls. Retinopathy prevalence increased with duration of diabetes in the diabetic group, with a prevalence of 1% from 0--4 yr after diagnosis, 25% after 5--9 yr, and 67% 10--16 yr after onset of the systemic disease. There was an independent association with age, with little retinopathy before age 15 and a 48% prevalence in older persons. Retinopathy was also found to be independently associated with the following: diabetic "control," evaluated semiquantitatively but on a masked basis; lens opacities; and frequency of daily insulin injections. Among the 166 diabetic subjects who had both angiography and photography, a retinopathy prevalence of 17% was detected by angiography and 11% by photography. This difference was statistically significant (P = 0.01). This study provides baseline data for use in estimating sample size in controlled trials of therapeutic measures to prevent retinopathy in juvenile diabetic populations. The study also supports the hypothesis that long-term hyperglycemia as well as changes (possibly hormonal in nature) associated with puberty are causally related to diabetic retinopathy.

Adolescent↗