Lens and eye toxicity research最新文献

Results of measurements of the transmission (total and in line) of cataractous lenses are presented. A magnitude is introduced which can be used as a measure of the in vitro opacity of lenses.

The IR technique has been applied to investigate secondary structure of the crystallins from the normal bovine eye. Crystallins have been isolated by column chromatography. IR spectra were recorded for the solid phase of proteins. From these spectra, especially amide I, amide II and amide V bands, the presence of alpha-helix, beta-sheet, beta-chain and unordered structures is stated. It was elucidated that alpha-crystallins are present mainly in a beta-sheet conformation but they also contain a considerable quantity of alpha-helix and a slight quantity of unordered and beta-chain forms. In beta H-crystallins, alpha-helix and, in a lesser percentage, beta-structures predominante. beta-sheet, alpha-helix and a low content of beta-chain forms are present in beta L-crystallins. In gamma-crystallins all forms secondary structure have been found, with predominance of beta-sheet and alpha-helix forms. A satisfactory agreement has been noticed between the forms of secondary structures in crystallins investigated by the IR technique and the results obtained by means of other methods. In conclusion IR spectroscopy has been suggested to be applied to observe crystallin structure during formation and development of a cataract.

Previous work from this laboratory has suggested that a lens regulatory protein, RF-36, possesses pleiotropic function in a homeotic switch during lens growth and differentiation. Evidence for this was derived from its interaction with specific receptors on the cell surface. Within minutes after incubation in lens cell culture system, enhanced membrane protein phosphorylation occurred. This process apparently activated at least two kinase-like activities, e.g. General kinase C and tyrosine kinase. The molecular weight of the phosphorylated protein was found to be 26kDa. Immunological studies indicated that the 26kDa component is part of the so-called "MIP" intrinsic membrane protein. Compared with other oncogenic proteins, there are no structural similarities between RF-36 and oncogenes. These data strongly suggest that RF-36 has a major pleiotropic function as a special kind of informational molecule; that is, a chemical messenger in promoting signal transduction in lens tissue.

In order to investigate the binding affinities of ocular lens glutathione S-transferases for non-substrate ligands we have studied the inhibition of bovine lens GSTs by physiological ligands, hematin, bilirubin and the xenobiotic bromosulfophthalein. Hematin was found to be a strong inhibitor as compared to bromosulfophthalein and bilirubin for the two lens isoenzymes, GST 7.4 and GST 5.6, both of which belong to the mu class of GSTs. Except for the competitive inhibition of GST 5.6 by hematin both the isoenzymes were inhibited non-competitively by these compounds. These results indicate binding of these non-substrate ligands to lens GSTs and suggest that similar to the extra ocular GST, the lens GSTs also play a role in the detoxification of hydrophobic compounds through non-catalytic binding.

A simple two phase model does not explain the temperature dependence of T1 relaxation time in lenses as biological systems. Therefore, a distribution of correlation times of water particles has to be assumed by a certain distribution of the water protein binding energy. As a consequence, from the temperature dependence of T1 relaxation time, the activation energy of water molecules in the lens cannot be evaluated directly without the knowledge of the distribution width. This problem can be solved by T2 measurements in lenses. From the slope of T2 as a function of temperature, mean activation energy can be calculated independently on the distribution width. Measurements were performed on lenses originating from 5-7 years old cows, 2-year old bull-calfs and a 12-year old bull in the temperature range -30 to +105 degrees C. It could be demonstrated that about 80% of water behaves as liquid-like water with an activation energy 14 +/- 4 kJ/mol corresponding to the value of free water. The remaining water (about 20%) is bound to the protein with an activation energy of 20 +/- 5 kJ/mol. At 42 degrees C the protein denaturation process starts in the eye lens and will be completed by 70 degrees C, yielding a protein bound-water complex.

Energy dispersive x-ray microprobe analysis was used to determine the distribution of chloride, potassium, phosphorus and sulfur in the epithelial cells of the lenses obtained from 3 to 7 month old Emory mice and 7 month old cataract resistant strain of Emory mice. Rapidly frozen lenses were fractured in the frozen state and lyophilized. The anterior epithelial cells were analyzed from equator to equator. The results show that the epithelial cells of the 7 month old Emory mouse lens have considerably higher amounts of chloride, sulfur, potassium and phosphorus. Presence of increased amount of potassium in the epithelial cells is intriguing. The data obtained from these experiments show that the changes in the elemental levels of epithelial cells are similar to observed alteration found in the lens fiber mass of 7 month old Emory mouse.

Using the angular dependence of intensities of light scattered on sections of bovine lenses, we have determined correlation lengths related to the scattering samples. The correlations were calculated on the basis of random density and orientation fluctuation theory. The lenses were classified by means of an instrument for the measurement of transmission and the unscattered component of light. The correlation lengths are compared with dimensions of aggregates.

The lens is an important element in the optical system of the eye. It has a gradient of refractive index for purposes of aberration control and in order to provide the ocular system with sufficient power. The lens also contains unique structural proteins. Although much work has been done to characterize the lens proteins, a structure/function relationship between these entities and the optics of the normal lens had not been previously considered. To investigate if such a relationship exists, biochemical and optical investigations were carried out under the common theme of development and aging. Investigations of distribution patterns of the three protein classes and measurements of the refractive index gradient were made on bovine and human lenses over wide age ranges. The results of these studies were compared. Although there was no direct evidence of a link between a single protein class and the index gradient, there are hints from interspecies comparison, that the level of LMW proteins may determine the magnitude of the refractive index. It is also possible that the insoluble fraction, which bears the greatest relationship in trend to the refractive index gradient, may represent proteins (largely pounds-crystallins) which have been structurally altered in situ in order for the lens to maintain viable optical function under the conditions of continual growth and aging.

This preliminary report has two parts. The first is based upon data obtained from a group of cataract patients in southern Florida (USA) with the object of relating the types of cataracts removed to their personal background and their protein biochemistry. Intra-capsular cataract surgery patients at the Venice Eye Clinic (Florida) were interviewed, and their extracted lenses were classified. The parameters were: age, place of residency, occupation, medical and family history and indoor/outdoor activity. Subcapsular cataracts were found mainly in the youngest patients and in those who were in Florida the least. Mixed cataracts predominated in the oldest patients, while non-nuclear cataracts were associated most with outdoor activity. Water-insoluble protein was elevated in nuclei of lenses with nuclear opacities. Soluble proteins in the nuclei of nuclear cataracts had increased levels of voided (heavy) protein, beta-crystallins, and less than 20 Kd peptides. The above changes were enhanced in brunescent cataracts. In lenses with cortical opacities, only increased size heterogeneity in the beta-crystallin region was observed. The second part of this report is based upon direct measurements of the optical properties of freshly extracted intra-capsular cataracts obtained in Rochester, New York (USA). The purpose was to attempt to learn the relative contributions that absorption, scattering, and fluorescence make toward obscuring vision. A general conclusion is that the shorter wavelengths of radiant energy in environmental lighting influence the above-stated optical properties the most, and thus appear to be the major contributors to obscured vision.