ISSN:0271-3683    

DOI:10.3109/02713688408997181

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

The chemical composition and morphology of the cornea and lens can provide significant information regarding what wavelengths of non-ionizing radiation these two tissue should absorb and transmit. Such data, including a variety of parameters determined by biophysical techniques, can provide us with information regarding the molecular basis for corneal and lenticular transparency and the subtle changes occurring with aging and ambient radiation exposure during our lefetime. The biophysical approach (fluorescence and NMR spectroscopy) has already provided new clinical tools for studying and delineating the initial events responsible for eventual opacification in these two tissues, months to years before they become manifest by current conventional clinical methods of examination.

ISSN:0271-3683    

DOI:10.3109/02713688408997182

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

During the aging process, the lens is subjected to changes of its pertinent properties which condition the transmission of light of different wavelengths. Between the second and the third decade, for instance, wavelengths below 400 nm are almost completely absorbed. The increase in lens thickness, effected by the appositional growth during life, might be considered responsible for this phenomenon, if the newly developing lens fibers in the outer periphery would synthesize proteins which, with respect to light transmission, differ from those formed during the embryonic phase. For such a phenomenon, however, no indication was found either by clinical observations or biochemical research. -Microdensitometric analysis of Scheimpflug-photographs of the anterior eye segment allows measurements of lens transparency in the single lens which directly depend on the respective wavelengths used in the photographic procedure. Investigations performed with this method on a normal age-grouped population, show that the changes in light transmission are most evident in two of the lens segments. The lens nucleus shows a continuous increase in light scatter during aging. Also the anterior cortex–particularly in the deeper layers–shows changes in light transmission. With advancing age (beginning between 30 and 40 years of age), increased lens fluorescence is found in the region of the deeper anterior cortex, which can be excited by UV wavelengths of 330–380 nm. This phenomenon is not found in the lens nucleus. The localization of the changes within the lens clearly shows that they are due to age-related modifications of the protein properties earlier designated as posttranslational or postsynthetic molecular modifications. A series of chemical reactions responsible for such modifications are also already known. Since the changes of light transmission in lens nucleus and anterior (deeper) lens cortex are of different quality, it may be supposed that different mechanisms are involved in the respective postsynthetic protein changes. With respect to the lens nucleus, it may be assumed that the formation of aggregates leading to high molecular weight proteins play a role, while in the lens cortex mostly oxidative changes are responsible.

ISSN:0271-3683    

DOI:10.3109/02713688408997183

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

Ultraviolet light can result in corneal, lenticular and retinal damage; however it can also be used (at much lower intensities) to measure the light induced alteration of cellular respiration and function. Mitochondrial function can be measured by noninvasive redox fluorometry which measures the intrinsic mitochondrial fluorescence of the reduced pyridine nucleotides (NADH + NADPH) and of the oxidized flavoproteins. Impaired mitochondrial respiration results in an increase in the reduced pyridine nucleotide fluorescence signal (366 nm excitation and 450 nm emission) and in a decrease in the oxidized flavoprotein fluorescence signal (450 nm excitation and 550 nm emission). These redox signals are sensitive to the cellular supply and utilization of oxygen and glucose as well as the mitochondrial work load. The effects of a reduced oxygen supply to the corneal epithelial surface can be measured. While redox fluorometry has been applied to the study of corneal hypoxia, it may also be used to monitor the effects of light induced damage to the lens and the retina. Non-invasive redox fluorometry is a sensitive technique to measure the effects of light on mitochondrial function in ocular tissue.

ISSN:0271-3683    

DOI:10.3109/02713688408997184

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

This paper presents a review of ultraviolet induced corneal effects which have been observed in the primate eye. Data discussed include the action spectra for far- and near-UV induced corneal damage, the pulsewidth dependence and oxygen dependence of near-UV corneal thresholds, and recovery rates of corneal epithelial damage following ultraviolet induced cell lethality. In addition, retinal photoreceptor damage induced by near-UV radiation is described.

ISSN:0271-3683    

DOI:10.3109/02713688408997185

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

The mechanism of oxidative damage to the lens through intraocular photochemical generation of superoxide and its derivatization to other oxidants such as singlet oxygen, hydroxyl radical and hydrogen peroxide has been studied. Rat lenses when organ cultured aerobically in TC 199 containing additional amounts of riboflavin were damaged as demonstrated by an inhibition of the uptake of Rb 86 against a concentration gradient. The pump was not affected by light if the culture was conducted in the basal TC 199. However, light was observed to induce significant peroxidative degradation of the tissue lipids even in the basal medium, the degradation being indicated by the formation of malonaldehyde. Both the inhibition of the pump as well as the peroxidative degradation of the tissue lipids, were attenuated considerably by scavengers of superoxide and hydrogen peroxide. In addition, the lipid degradation was prevented by vitamins C and E. The results suggest that the photodynamic injury to the lens cation pump as well as to membrane lipids is incumbent upon an initial generation of superoxide and its derivatization to other oxidants. Thus, the ocular lens is susceptible to oxidative insult and physiological damage through photo-catalytic generation of various oxygen radicals. Large concentrations of ascorbic acid in the aqueous humor seems to be able to provide significant protection against such an insult. Thus, this may be one of the functions of high concentration of ascorbic acid in the aqueous humor.The implication of oxidative stress has also been examined in the genesis of cataractsin vivo.Treatment with vitamin E of the Emory mouse led to a decrease in the rate of cataract progression suggesting that at least in some instances an oxidative stress could participate in the formation of cataracts. Oxygen radicals may inflict damage at multifarious biochemical sites. Human lens lipids were also shown to have an absorption maxima at 239 nm indicating their susceptibility to oxidative degradation. In addition the lipid extract has fluorescence similar to that of lipofuscins. The levels of MDA were higher in the brunescent cataracts as compared to that in the nonbrunescent cataracts. The implications of oxidative stress towards the genesis of cataracts in humans is being explored further.

ISSN:0271-3683    

DOI:10.3109/02713688408997186

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

The effects of photodynamically generated singlet oxygen on lens crystallins were investigated. This highly reactive oxidant can produce in crystallins in vitro the oxidative modifications characteristic of proteins from aging and cataractous lens. Additionally species capable of producing singlet oxygen in the presence of near UV radiation are shown to be present in human lenses. These findings are discussed with respect to a possible role of singlet oxygen in the etiology of human senile nuclear cataracts.

ISSN:0271-3683    

DOI:10.3109/02713688408997187

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

A free radical mechanism of cataractogenesis involving enzymatic and nonenzymatic reactions, is proposed. Supporting experimental evidence is briefly reviewed. H2O2, which is one of the toxic metabolites of oxygen, was significantly increased 2–3 fold in ocular humors in several experimental cataracts and in human senile cataract. Various cataractogenic agents were also found to increase H2O2in ocular humorsinvivoprior to cataract formation. Enzymatic defenses against O2·- and H2O2provided by superoxide dismutase, catalase and glutathione peroxidase were impaired in cataracts. In some cataracts, catalase and superoxide dismutase were affected earlier. Malondialdehyde (MDA), a major breakdown product of lipid peroxides was significantly increased by 2–4-fold in human senile cataract, in cataracts induced in rabbit and rat, and in hereditary cataracts in mice. All the reactive species of O2(O2·-, H2O2, OH·and1ΔgO2) may participate in initiating lipid peroxidation of lensin vitro.Various scavengers of these species were capable of preventing lenticular lipid peroxidation, amongst which OH·scavengers were found to be the most effective. Biological antioxidant, vitamin E afforded 44% prevention of lipid peroxidation in lens. The important observation was that vitamin E was therapeutically effective in about 50% of animals in arresting cataract induced in rabbit by 3-aminotriazole. In these rabbits, H2O2and ascorbic acid of ocular humors and MDA of lens were close to normal.It is our working hypothesis that the carbonyl groups of MDA and amino groups of amino acids, proteins, nucleic acids and their bases, and phospholipids could interact in a cross-linking reaction producing high molecular weight aggregates by Schiff-base conjugate formation in addition to disulfide cross-linking of proteins, and finally resulting in cataract.

ISSN:0271-3683    

DOI:10.3109/02713688408997188

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

Glutathione is present in both the reduced and oxidized form in the cornea, aqueous humor, ocular lens and retina. In these tissues it serves a variety of functions including maintaining normal tissue hydration (in the cornea) detoxifying peroxides and electrophilic compounds via enzymatic pathways and acting as a free radical scavenger to protect against photoinduced damage.In the ocular lens, glutathione levels decrease with aging and cataract formation. Recent evidence which may account in part for this phenomenon suggests that glutathione is altered when subjected to UV radiation in the presence of H2O2. Analyses employing fluorescence, phosphorescence, UV absorption and proton mode NMR spectroscopy demonstrate that UV exposure does alter both the reduced and oxidized forms of glutathione, producing the same final products. Moreover, while H2O2speeds up the process, it is not essential to the reaction.

ISSN:0271-3683    

DOI:10.3109/02713688408997189

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor

摘要:

Six factors were analyzed which may be involved in the decline of glutathione synthesis in the aging lens and cataract, with special emphasis placed upon the human lens. The factors included: 1) lability ofγ- glutamylcysteine synthetase, 2) paucity ofγ-glutamylcysteine synthetase in primate lenses as compared to other mammalian lenses, 3) enzyme activity reduction with age in the human lens, 4) rate control by reactant scarcity, especially of cysteine and magnesium ion, 5) rate control by inhibition using 5′-AMP, 5′-ADP and glutathione, and 6) possible dissociation of the multi-enzyme complex. It was concluded that decline of the glutathione synthetic capacityin vivowould be most likely caused by reduction ofγ-glutamylcysteine synthetase activity rather than of glutathione synthetase activity.

ISSN:0271-3683    

DOI:10.3109/02713688408997190

出版商:Taylor&Francis    

年代:1984

数据来源: Taylor