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Biomedical subjects

S Zigman

Publications and source records attributed to S Zigman.

At least 55 records · Page 3Linked to original sources
PubMed1985

Biochemical features of the grey squirrel lens.

The ocular lens of the grey squirrel (Sciurus carolinensis) is an excellent model for studies of eye-light interactions that apply to the human system. In this diurnal animal, lens size, shape, yellow pigmentation, and light absorption properties have important similarities to those of young children. This article describes the observations of soluble to insoluble protein conversion with chronological aging, and the loss of heavier lens crystallins in the internal as compared to the external layers of the lens. Such changes are related to aging, as the older lens material is present in the nuclear core, while the younger lens material is superficial. It describes the subunit peptides of the soluble crystallins and of the extrinsic and instrinsic proteins associated with fiber cell membranes. Squirrel lens fiber membranes release most of their extrinsic peptides in 8 M urea, as do those of other young animals. Due to the presence of near-UV absorbing species of low molecular weight, the squirrel lens has great potential for studies of the effects of near-UV radiation on the lens.

Animals↗
PubMed1984

Effects of H2O2 on the dogfish (Mustelus canis) ocular lens.

The influence of in vitro exposure of dogfish (Mustelus canis) lenses to H2O2 was studied. Concentrations of H2O2 greater than 10(-4)M caused opacities in the outer cortex of the lens within a few hr. Evidence of protein aggregation within the lens and in extracted lens protein solutions was found. Dithiothreitol inhibits aggregation. Little if any influence of H2O2 was observed on 86Rb exchange of the dogfish lens.

Animals↗
PubMed1984

Lipids of human lens fiber cell membranes.

A study of the membranes of human lens fiber cells revealed a very high protein to lipid ratio, which tended to increase with aging and in brunescent cataract. Phospholipids were more abundant than cholesterol, cholesterol esters, and other neutral lipids. With aging and cataract formation, a marked decrease in membranes phospholipid content occurred. Sphingomyelin was present in highest amount. Phosphatidylethanolamine, phosphatidylcholine, lysophosphatidyl-ethanolamine, phosphatidylserine, and phosphatidylglycerol were also present. Cholesterol represented approximately 40% of the total lipids. Saturated and unsaturated fatty acids having 16 to 24 carbons were present. The lipid composition varied according to the portion of the lens examined and the state of the lens. The results do not support a conclusion that lipid peroxidation represents a major mechanism of membrane damage that contributes to cataract formation, since there is no decrease in unsaturated fatty acids with age or in cataractous lenses. We suggest that the aggregation of soluble proteins, and their association with lens membranes, and altered membrane function due to the loss of phospholipids are important processes leading to loss of transparency.

Adult↗
PubMed1983

Effects of near ultraviolet radiation on the lens and retina.

This communication represents a consideration of non-visual interactions between environmental light and the eye. It covers the following topics: light in the environment; light entering the eye and transmission to the retina; observed light damage; mechanisms of light damage; and considerations of the absorptive properties of artificial lenses. The intention of this paper is to summarize the available information and some of the current thinking about the non-visual interactions of the eye with short wave-length radiation. Many more experiments must be done for us to appreciate the full significance of this information for the benefit of man.

Adolescent↗
PubMed1983

A comparative study of lens gamma crystallins using isoelectric focusing.

The isoelectric points of gamma crystallins of the lenses of rats, dogfish, calves, and humans differ, with a range of pH 8.87-6.80. In each species, one gamma crystallin component with an isoelectric point at pH 7.5 is present, but at differing levels. Amino acid compositions of this component were similar among these four species. All pH 7.5 isoelectric point proteins crossreact immunochemically. A common messenger RNA must be present for this gamma crystallin in all of these species.

Aged↗
PubMed1982

Tinting of intraocular lens implants.

Intraocular lens (IOL) implants of polymethyl methacrylate (PMMA) lack an important yellow pigment useful as a filter in the visual process and in the protection of the retina from short-wavelength radiant energy. The ability to produce a yellow pigment in the PMMA used in IOL implants by exposure to near-ultraviolet (UV) light was tested. It was found that the highly cross-linked material in Copeland lens blanks was tinted slightly because of this exposure. The absorptive properties of lens blanks treated with near-UV light in this way approached that of the absorptive properties of human lenses. This finding shows that it is possible to alter IOL implants simply so as to induce a pale-yellow pigment in them to improve the visual process and to protect the retinas of IOL users.

Color↗
PubMed1982

Stability of shark and human lens fiber cell membranes.

1. Scanning electron microscopy of minced dogfish, shark, and human lens fiber cell preparations showed that neither 8 M urea or 1% SDS was capable of totally disrupting the fiber cells, but that their membranes were totally disrupted by 1% SDS containing 50 mM dithiothreitol. 2. Fiber cells were purified by sucrose centrifugation and extracted with Tris-buffer, 8 M urea, 1% SDS and 50 mM dithiothreitol plus 1% SDS. 3. A residual 10% of the protein was capable of maintaining membrane integrity. 4. DTT + SDS totally dissolved the membranes, implying that disulfide bonds are involved in maintaining structure. 5. Non-tryptophan fluorescence was nearly totally extracted prior to the SDS-DTT step, indicating that the fluorescence associated with the membrane protein was not serving as crosslinks between extrinsic and intrinsic proteins. 6. Polyacrylamide slab gel electrophoresis revealed that after exhaustive extractions of lens fiber cells with Tris-buffer, 8 M urea and 1% SDS, the addition of DTT released major heat stable 27,000 and 24,000 dalton peptides. 7. The data support the concept that fiber cell membranes contain high levels of extrinsic peptides and intrinsic peptides whose stability depends strongly on oxidized crosslinks, probably disulfide bonds.

Animals↗
PubMed1982

Sub-threshold near-UV radiation effects on aphakic guinea pig retinas.

Monocularly aphakic guinea pigs (Cavia porcellis), prepared by removing the lens by phacoemulsification, were maintained under near-UV lighting conditions for several months. Exposure to near-UV energy was at much lower irradiance levels than that of sunlight, and was at lower than the threshold level for near-UV damage to the aphakic monkey retina as reported by Ham, et al (1). In some aphakic eyes, regenerated lens-like structures formed which scattered light appreciably. After increasing light exposure periods, the eyes of control and irradiated animals were studied histologically. Other animals were periodically examined by electroretinographic (ERG) techniques. While there was no observable histopathological damage, aphakic-UV irradiated eyes with little or no lens regrowth exhibited depressed b-waves, late time constants and altered wave forms when compared with control eyes. The results demonstrate that ambient near-UV light exposure can adversely influence retinal electrical activity in aphakic eyes at irradiance levels below threshold for morphological damage. The protective function of the lens is also supported by these findings.

Animals↗
PubMed1981

Lack of photosensitization of ocular tissues by allopurinol.

Based on careful double-blind studies using albino mouse ocular tissues, we conclude that allopurinol does not act as a photosensitizer for ocular tissue damage in mice relative to exposure to environmental near ultraviolet (UV) light. Damage to lens epithelial cells and retinal photoreceptors was equivalent in UV light-exposed mice that were either fed or not fed a dose of allopurinol equivalent to that used by humans in the treatment of gout. There was also no direct in vitro photosensitizing interaction between allopurinol and protein or nucleic acids. We conclude that patients in whom cataracts developed after using allopurinol and exposure to high irradiances of near UV light were most likely affected by the UV light itself.

Allopurinol↗
PubMed1980

Inhibition of cell division and growth by a redox series of cyanine dyes.

A series of cyanine dyes used in photography, with reduction potentials from -1.35 to -0.20 volts, were tested for their ability to inhibit mitosis and cell growth in fertilized sea urchin eggs. Low concentrations of dyes with reduction potentials more negative than -1.0 volt generally inhibited mitosis and growth, whereas those with more positive reduction potentials did not. The active dyes penetrated the cell, entered all subcellular compartments, were bound to numerous macromolecules, and inhibited synthesis of macromolecules. Thus mitosis and growth may be retarded with substances that can alter electrochemical activity in cells.

Animals↗
PubMed1979

Eye lens ageing in the dogfish (Mustelus canis).

1. Age-related alterations in the distribution of water-soluble, high molecular weight (colloidal), and water-insoluble proteins of the lens of smooth dogfish (Mustelus canis) were measured. 2. The ages of these animals ranged approx from 2 to 50 yr, during which time the lenses grew from 100 to 1500 mg (wet wt). The lenses contained approx 50% water. 3. Water-insoluble protein accumulated to a level greater than 50% of the total proteins by the time the animals reached maturity. The lenses of other animals, such as mammals and humans, would be opaque if they had a similar insoluble protein content. 4. Each protein fraction contained the same protein chains (mol. et 1900-25,000 daltons), as observed by SDS polyacrylamide gel electrophoresis, except the water-insoluble fraction, which seemed to contain several extra protein chains with higher molecular weights, which represent fiber cell membrane components. 5. Further purification of these fiber cell membranes indicated that their protein chain makeup was mainly from the same low molecular weight chains present in the soluble and high molecular weight colloidal proteins.

Aging↗
PubMed1979

Sunlight and human cataracts.

Studies of the cataractous lenses of humans in three different geographic locations indicate that where the ultraviolet components of sunlight are more intense, dark brown cataracts result at a higher frequency than in locations where they are weak. Individuals exposed to sunlight regularly by virtue of their outdoor occupations seemed to develop this dark brown type of cataract much more frequently than those who work indoors. The biochemical characteristics of all brunescent cataracts were found to be very similar, whether derived from individuals exposed to high or low levels of sunlight. These findings support the idea that exposure to sunlight specifically enhances brunescent cataract development in humans.

Adult↗