Syneretic response to incremental pressures in calf lenses.

Purpose: Syneretic response to pressure variation of 1 atm or more has been demonstrated previously in bovine and human lenses with nuclear magnetic resonance (NMR) relaxation measurements. This study is designed to prove that a similar response is observable in smaller pressure increments closer to the normal physiological range.

Methods: Excised calf eyes were enucleated, the lenses dissected out, and immersed in medium.

Alterations in human vitreous humour following cataract extraction.

Cataract extraction is associated with the risk of posterior vitreous detachment, macular edema and retinal detachment possibly as a result of a disturbance to the vitreous body during surgery. While it is common for lens cortical fiber debris to leak into the vitreous humour during cataract extraction, the extent to which the vitreous humour is altered post-surgery is unknown. The current study examines the integrity of the vitreous humour of pseudophakic and phakic human donor eyes by comparing the proteome, the viscosity and the size distribution of macromolecules in different regions of the vitreous humour from human pseudophakic and phakic donor eyes.

Light scattering in lens research: an essay on accomplishments and promises.

This paper briefly reviews light scattering methodologies in lens research. In the phenomenological sense cataract formation (lens opacities or turbidities) in its early stages can be described by enhanced scattering of light. In the analytical sense information is obtained on the molecular entities involved in light scattering.

Regional mapping of molecular components of human liquid vitreous by dynamic light scattering.

The distribution of particle sizes was studied in six regions of human liquid vitreous samples. Particle sizes were calculated from dynamic light scattering measurements as hydrodynamic diameter of molecules. In general, particle sizes increased progressively from anterior (near lens) to posterior (near retina).

Syneretic response of aging normal human lens to pressure.

Purpose: The study was designed to observe whether a reversible syneretic response to pressure is operative in normal human lenses and whether such a response demonstrates a uniform age dependence.

Methods: Seven sections (from the anterior outer cortex to the posterior outer cortex) of 10 human lenses were imaged at 2 atmospheres (atm) pressure and the T(1) (spin-lattice) and T(2) (spin-spin) relaxation data on each section were collected. The pressure was then released and NMR relaxographic data were collected under 1 atm.

Relaxographic studies of aging normal human lenses.

Ten excised normal human lenses of various ages were studied. Seven sections of each lens, from anterior outer cortex to posterior outer cortex were imaged and the T(1) (spin-lattice) and T(2) (spin-spin) relaxation data on each section were collected. T(1) and T(2) relaxation were analysed by fitting pixel intensity to one term exponential expressions.

Kinetics of chaperoning of dithiothreitol-denatured alpha-lactalbumin by alpha-crystallin.

Molecular chaperones prevent the aggregation of partially folded or misfolded forms of protein. alpha-Crystallin performs such a function in the ocular lens. Dynamic light scattering (DLS) measurements were performed to gain insight into the kinetics and mechanism of alpha-crystallin chaperoning.

NMR relaxation studies of syneretic response to pressure change in bovine lenses.

Purpose: Reversible syneretic response to pressure in bovine and rhesus monkey lenses has been demonstrated previously by invasive techniques, such as differential scanning calorimetry and thermogravimetric analysis. This study is designed to investigate whether such a response could be observed by non-invasive techniques, namely by relaxographic imaging studies, in situ, in the intact, albeit excised lens.

Methods: Excised bovine lenses were incubated in media at 37 degrees C in specialized pressure chambers for 24 hrs.

Syneretic response to pressure in bovine and rhesus monkey vitreous.

Excised bovine and rhesus monkey vitreous samples were subjected to different hydrostatic pressures (0.03, 1 and 2 atm) for 12 hr. At the end of the experiment the samples were frozen in a -70 degrees C dry ice-acetone bath and thereafter maintained in frozen conditions.

On the equilibrium between monomeric alpha-lactalbumin and the chaperoning complex of alpha-crystallin.

In chaperoning dithiothreitol-denatured alpha-lactabumin, alpha-crystallin forms a chaperoning complex. In order to study the kinetics of such chaperoning it needs to be established whether the formation of the chaperoning complex is a reversible or irreversible process. The chaperoning reaction was studied by dynamic light scattering as a function of concentration and weight ratio of alpha-lactalbumin/alpha-crystallin.

The mode of chaperoning of dithiothreitol-denatured alpha-lactalbumin by alpha-crystallin.

Molecular chaperones prevent the aggregation of partially folded or misfolded forms of protein. alpha-crystallin performs such a function in the ocular lens. To gain insight into the mechanism of the anti-aggregation activity of alpha-crystallin, we performed dynamic light scattering (DLS) measurements investigating its interaction with partially denatured alpha-lactalbumin over a 24 hr period.

Pressure-induced syneretic response in rhesus monkey lenses.

Purpose: To investigate the effect of pressure on the freezable and nonfreezable water content of the lens.

Methods: Excised rhesus monkey lenses in tissue culture media were subjected to three different hydrostatic pressures (2 atm, 1 atm, and 0.03 atm) for 24 hours.

Do changes in the hydration of the diabetic human lens precede cataract formation?

Cataract formation in diabetic lenses has been attributed to polyol-osmotic pressure-generated influx of water. The ensuing swelling in the form of pocket and lake accumulations cause light scattering. The authors tested whether clear lenses of diabetic patients show different hydration properties than age matched normal lenses.

Thermodynamic stability of bovine alpha-crystallin in its interactions with other bovine crystallins.

Light scattering measurements were performed on dilute solutions of alpha-crystallin mixed with different combinations of beta H, beta L and gamma-fractions of bovine lens crystallins. Light scattering intensities were obtained as a function of scattering angle, concentration and temperature. The temperature dependence of the second virial coefficients was used to obtain partial molar enthalpy and end entropy of solutions.

Role of small GTP-binding proteins in lovastatin-induced cataracts.

Purpose: To investigate the biochemical mechanisms involved in the cataract induced by lovastatin, a commonly used cholesterol-lowering agent.

Methods: The effects of lovastatin on lens transparency and on lens epithelial cell proliferation and structure have been investigated using organ-cultured rat lenses and cultured epithelial cells from human and rabbit lenses, respectively. Lens histologic and morphologic changes were recorded microscopically.

On the nature of hereditary cataract in strain 13/N guinea pigs.

Purpose: Congenital nuclear cataracts in strain 13/N guinea pigs are caused by a single splice-site mutation in the zeta-crystallin gene. Very little is known of the physical factors involved in lens opacification of this system. The aim of this study is to elucidate the biophysical processes causing the nuclear turbidity.

Light scattering and morphology of cataract formation in transgenic mice containing the HIV-1 protease linked to the lens alpha A-crystallin promoter.

Two constructs of transgenic mice, TG61 and TG72, containing the HIV-1 protease linked to the lens alpha A-crystallin promoter develop cataract. The TG61 construct develop cataract in utero, while the TG72 construct exhibit frank opacities on the 24th day (homozygotes) and 26th day (hemizygotes) post natum. Polarized light scattering measurements were performed on cortical and nuclear sections of TG72 lenses from day 19 to day 26 as a function of scattering angle.

Light scattering parameters of rat lenses with calcium-induced cataracts.

Light scattering intensities of rat lenses obtained in the I,, and I+ modes were analysed using the random density and orientation fluctuation theory. Rat lenses incubated in calcium rich media had the same density fluctuation parameters as rat lenses incubated in control (low-calcium) media. However, the correlation length of the orientation fluctuations decreased during cataract formation by 100 to 200 nm while the amplitude of the fluctuations increased.

Degradation of vimentin in frozen rat lenses.

Rat lenses stored for extended periods at -20 degrees C showed degradation and eventual disappearance of vimentin. This may have been caused by the rupture of cells and/or organelles by growing ice crystals and the subsequent release and diffusion of proteases. Besides the disappearance of vimentin there was also a decrease in the intensity of the beta B1 polypeptide after 3 months storage.

Lens hydration in transgenic mice containing HIV-1 protease linked to the lens alpha A-crystallin promoter.

Two constructs of transgenic mice, TG61 and TG72, containing HIV-1 protease linked to lens alpha A-crystallin promoter develop cataract. The TG61 construct exhibits cataractogenesis in utero, while in the TG72 construct frank opacities appear 24 days (homozygotes) and 26 days (hemizygotes) after birth. Differential scanning calorimetry and thermogravimetric analysis studies indicate that the hydration of lenses is strongly correlated with cataractogenesis.

Enthalpy and entropy of hydration of bovine crystallins.

Transparency of the lens of the eye is the result of a short range order in the packing of crystallin molecules within the fiber cells. Short range order depends on crystallin-crystallin as well as water-crystallin interactions. Light scattering measurements can provide information on the hydration of crystallins.

A study of collagen-hyaluronan interaction through swelling in polyacrylamide gels.

The equilibrium swelling of biopolymer loaded polyacrylamide gels can yield information on polymer-polymer interactions. Using the temperature dependence of excess equilibrium swelling, equations were derived to yield homopolymer as well as heteropolymer interactions. Hyaluronan and collagen (Type I) encapsulated in polyacrylamide gels showed increasing isothermal swelling with increase in the bipolymer concentration.

Calcium cataract: a model for optical anisotropy fluctuations.

Young rat lenses were incubated in organ culture media enriched with 20 mM calcium. Lenses in the calcium rich medium developed cataracts and were characterized by the absence of vimentin in the urea soluble protein fractions. Sections from the same lenses were studied by polarized light scattering.