Quantitative analysis of animal model lens anatomy: accommodative range is related to fiber structure and organization

PURPOSE

The results of a recent study on accommodation in humans and baboons has revealed that lens fiber structure and organization are key components of the mechanism of accommodation. Dynamic focusing involves the controlled displacement and replacement, or realignment, of cortical fiber-ends at sutures as the mechanism of accommodation at the fiber level. This emended explanation of the mechanism of accommodation raises the following question: as the structure of crystalline lenses are only similar, not identical between species, is accommodative amplitude related to differences in the structure and organization of fibers between species? To address this question, we have quantitatively examined the structure and organization of fibers in a number of the more commonly used animal models (mice, cattle, frogs, rabbits and chickens) for lens research.

MATERIALS AND METHODS

Lenses (a minimum of 12-18 lenses/species) from mice, cattle, frogs and rabbits were used for this study. Prior to fixation for structural analysis, measurements of the gross shape of the lenses (equatorial diameter, anterior and posterior minor radii [anterior + posterior minor radius = polar axis]) were taken directly through a stereo surgical dissecting microscope equipped with an ocular reticle. Lenses were then prepared for and examined by light (LM), transmission (TEM) and scanning electron microscopy (SEM). Scale computer-assisted drawings (CADs) of lenses and lens fibers were then constructed from quantitative data as described above and from quantitative data contained in micrographs.

RESULTS

The differences in fiber structure and organization that effect accommodative range arise early in development and are continued throughout lifelong lens growth. In umbilical suture lenses (avian) secondary fibers develop with almost completely tapered anterior ends (85-90% reduction of their measures of width and thickness at the equator). By comparison, in lenses with line sutures (e.g. frogs and rabbits) secondary fibers develop with just a 50-60% reduction in anterior fiber taper. In lenses with Y sutures (mice and cattle), fiber width taper is only 25-40%. However, in all cases, while the taper of the posterior end width of fibers is just slightly less (approx. 15-20%) than that of anterior ends, posterior end thickness is only reduced by one half that of anterior thickness.

CONCLUSIONS

In humans, the mechanism of accommodation at the fiber level involves the controlled realignment of very flattened and flared, rather than tapered fiber-ends at sutures. In this manner, the simultaneous increase in lens thickness and surface curvature in the accommodated state is the result of fiber-ends being overlapped along multiple (9-12) suture branches covering the majority of the anterior and posterior surfaces. The results of this animal study strongly suggest that accommodative range is directly related to quantitative differences in fiber structure and organization in the different suture types. The very broad accommodative range in birds is made possible, at least in part, by the almost complete tapering of fiber-ends at umbilical sutures. In contrast, the essentially negligible accommodative range of animals that have line- and Y-suture lenses is at least partially the result of the fact that these lenses have fibers with very little end taper. Thus, the blunt ends of fibers in line- and Y-suture lenses precludes any significant overlap of end segments to effect accommodation.

Fibre cell organization in crystalline lenses

This review qualitatively and quantitatively compares the gross shape and size of lenses from different species as a function of their fibre cell organization. Grossly, all vertebrate lenses are asymmetrical, oblate spheroids with size and spheroidicity that varies considerably between species. Correlative LM and SEM analysis of the basic structural element of lenses, the fibre cell, shows that the average equatorial fibre width and thickness is relatively constant between most species. This indicates that inter-species differences in lens size is primarily a function of fibre number. Comparable analysis demonstrates that lens spheroidicity is due at least in part, to differences in the average anterior and posterior fibre end segment thickness in relation to that at the equator. In addition, the above analysis, supplemented by 3D-CAD reconstructions, illustrates how lifelong lens growth produces crescent fibres, that become arranged in age-related, concentric growth shells overlaid in slightly imprecise register. The reason for the non-exact registering of growth shells is that, while the vast majority of fibres are hexagonal in cross-section, a very small minority are pentagonal in cross-section and of inconstant width and thickness. Hexagonal and pentagonal fibres are required because the increase in the circumference of successive growth shells is frequently less than the widths of hexagonal fibres. Thus, lens growth is likely accomplished by a combination of the addition of successive growth shells containing more fibres, as well as by the addition of growth shells containing equal numbers of fibres that are incrementally wider as a function of radial location. Finally, SEM analysis, supplemented by 3D-CAD reconstructions, highlights the fact that the end-to-end arrangement of fibres within growth shells, the suture patterns, is not identical in all vertebrate lenses. This is important because lens optical quality is directly related to lens suture type and a negative influence of sutures on lens optical quality increases with age and as a result of some ocular surgeries (vitrectomy and trabeculectomy). These facts suggest that future research efforts should be directed at determining the factor or factors that influence or direct the differences in fibre shape, size and organization in branched and unbranched suture lenses.

Suppression of post-vitrectomy lens changes in the rabbit by novel benzopyranyl esters and amides

This study reports for the first time a therapeutic modality for the suppression of posterior subcapsular cataract (PSC) formation in an animal model (rabbit) of vitrectomy. This therapeutic modality may also have the potential to attenuate/prevent the high incidence of loss of vision due to cataract formation in patients that undergo vitrectomy. Unilateral, partial vitrectomy was performed on 2.5 month old Dutch Belted rabbits with vitreous replaced by either commercially available BSS((R)) or BSS PLUS((R)) (n=16). Alternatively, vitreous was replaced with a proprietary, modified BSS PLUS((R)) irrigating solution containing 1.25 microM AL-8417 (n=12), 5.0 microM AL-12615 (n=5) or 5.0 microM AL-17052 (n=9). Age matched, non-operated rabbits were used as controls (n=16). Lenses were analysed by correlative structural (light, scanning electron microscopic and three-dimensional computer-assisted drawings) and optical (low power helium-neon laser scan) quality analysis 6 months following surgery. Results demonstrate that vitreous replacement with an irrigating solution that contains the ester-linked benzopyran, AL-8417, the amide-linked benzopyran pro-drug, AL-17052, or its active metabolite, AL-12615, prevented abnormal post-vitrectomy lens growth, or fiber formation. Focal length variability (FLV) assessments (sharpness of focus) confirmed the beneficial drug effects detected morphologically, with FLV being essentially equal to that of age-matched, non-surgical controls. In contrast, lenses of animals with vitreous replaced solely with BSS((R)) or BSS PLUS((R)) exhibited significantly higher FLV than both age-matched controls and animals that underwent vitrectomy with drug-containing irrigating solutions. The ability of AL-8417, AL-17052 and its active metabolite, AL-12615, to suppress vitrectomy-induced posterior lens fiber changes appears to reside in their unique pharmacological profile, acting as antioxidant, anti-inflammatory and cytostatic agents.

A quantitative analysis of sutural contributions to variability in back vertex distance and transmittance in rabbit lenses as a function of development, growth, and age

PURPOSE

To correlate specific parameters of lens structure (anterior and posterior suture branch length and planar area) with variability in back vertex distance (BVD) and scatter in rabbit lenses as a function of development, growth, and age.

METHODS

Lenses from juvenile (n = 9), adult (n = 9), and aged (n = 10) New Zealand White rabbits were utilized in this study. After sacrifice, lens suture patterns were photographed using a stereo surgical dissecting microscope. Within 5 min of sacrifice, average BVD, variability in BVD, and scatter were assessed with a Scantox In Vitro Assay System. Laser beams were passed incrementally along anterior and posterior suture planes through right eye (oculus dexter, OD) lenses, and between suture planes through left eye (oculus sinister, OS) lenses. After fixation, lens axial dimensions and suture branch lengths were assessed and used to create scaled, 3-dimensional computer assisted drawings (3-D CADs) depicting gross lens shape and sutural changes throughout life.

RESULTS

Whereas average BVD only increased significantly as a function of growth, variability in BVD only increased significantly as a function of aging. However, anterior sutures exerted a greater influence on variability of BVD than posterior sutures throughout growth and aging. This difference is consistent with anterior suture branches being longer, or extending farther peripherally, than posterior sutures. Scatter was essentially unchanged between juvenile and adult lenses but significantly increased in aged lenses. Notably, posterior sutures effected a greater age-related increase in scatter than anterior sutures. This difference was consistent with the formation of numerous small, posterior subbranches and subplanes later in life. Structural analysis also suggested that asymmetric age-related lens compaction had occurred, predominantly affecting posterior lens dimensions.

CONCLUSIONS

Lens sutures significantly influence average BVD throughout development and growth, and variability in BVD throughout aging. In addition, even though the rabbit lenses appeared transparent throughout growth and aging, unequal length and area of anterior vs. posterior suture branches and planes respectively, as well as a greater degree of age-related posterior lens compaction, were factors contributing to increased scatter.

The effect of aging on glutathione peroxidase-i knockout mice-resistance of the lens to oxidative stress

Populations of control, C, and glutathione peroxidase-1 (GPx-1) knockout mice, K, were studied over a period of 2 years. No significant difference was observed between the C and K populations with respect to longevity, vitality, weight, lens biochemistry or morphology based on light and electron microscopy. It was concluded that under normal animal room barrier facilities, GPx-1 is not required. Furthermore, C and K lenses placed in organ culture and observed over a 24 hr period were indistinguishable. Organ cultured C lenses degraded medium H(2)O(2)levels at only a slightly greater rate than K lenses and this did not appear to change with age. However, tertiary butyl hydroperoxide (TBHP) was degraded less effectively by K lenses and this deficiency increased with age. No indication of change in redox non-protein SH (equivalent to GSH) status was observed between C and K whole lenses or epithelial cell fractions. With H(2)O(2)stress, the drop in C and K non-protein SH was comparable and there was little change with age. Examination of the impact of photochemical stress with 1.5 microM riboflavin and 4% O(2)upon choline transport indicated considerable damage with both C and K lenses, but little difference between the two populations until 1 or 2 years of age when the K lenses appear more vulnerable. With TBHP, the detrimental effect on the K lenses is greater and is observed earlier than with photochemical stress suggesting that the K lens membrane function is more susceptible to phospholipid hydroperoxide stress than are C lenses. Light and electron microscopy of the oxidative stressed lenses indicates significant damage which was generally somewhat greater in the K lenses. TBHP was a more potent oxidant than photochemically generated oxidants particularly at the anterior pole. The overall results suggest that under normal conditions, at any age, the lens does not require the presence of GPx-1 but depending on the type of oxidative stress, the enzyme may significantly contribute to its defense and this dependency may increase with age.

Structural evidence of human nuclear fiber compaction as a function of ageing and cataractogenesis

This study was conducted to quantify structural change associated with human nuclear fiber compaction as a function of ageing and nuclear cataract formation. Normal donor lenses in three age ranges, young (15--25 years), middle-aged (36--46 years) and aged (59--81 years) were compared to each other and to age-related nuclear cataracts (55--81 years) surgically removed by extracapsular extraction. Several structural modifications which occurred as a manifestation of fiber compaction were noted. In the fetal nucleus (FN), the average anterior and posterior fiber angles decreased approximately 20% with age. Additionally, there was a reduction in the thickness of both the anterior and posterior segments of fetal fibers with age. On average, the anterior--posterior (A--P) axis in the embryonic nucleus (EN) decreased 33% with age. The average length of EN fibers decreased significantly (37%) as a function of age. This change in EN fiber length was accomplished by effecting compaction folds along fiber length. By comparison, in nuclear cataracts the anterior and posterior angles of FN fibers were about 12% smaller than comparably aged normal lenses. Similarly, the A--P axis and the length of EN fibers were 13% smaller than age-matched normals. Nuclear fiber compaction in early adulthood was significant and may contribute to the lens hardening and loss of accommodative ability symptomatic of presbyopia. 3D-CAD reconstructions of fiber compaction show how the reduction in the spacing of lateral interdigitations along fiber length causes an increase in the fiber membrane complexity along the A--P axis in relation to fiber cytoplasm as light passes through lenses. These results may explain, at least in part, how an increase in large particle scatter occurs as light is transmitted through fiber membranes, resulting in reduced lens optical quality as a function of age. By extrapolation, the significantly increased compaction of nuclear fibers in age-related nuclear cataracts may be a contributing factor for excessive scatter in nuclear opacification.

DeltaFosB-induced cataract

PURPOSE

The objective of this study was to investigate a possible relationship between posterior subcapsular cataract (PSC) formation and expression of the transcription factor DeltaFosB.

METHODS

Western blot analysis was performed on bitransgenic NSE-tTA, TetOp-DeltaFosB, and single-transgenic NSE-tTA control mice to determine the pattern of DeltaFosB expression within the eye. Light and scanning electron microscopy and biochemical analyses were also performed.

RESULTS

In mice expressing DeltaFosB, cataract developed that initially appeared to be posterior subcapsular and gradually matured to involve the entire lens. The enlarged posterior ends of developing secondary fibers curved away from the visual axis to form an elevated opaque posterior plaque. As a result, posterior suture formation did not occur. At a later time, the attenuated posterior capsule overlying the plaque ruptured and the lens nucleus subluxated into the vitreous. Retinal damage was also observed but only from postnatal day 65, a time when extensive lens degeneration had already occurred. DeltaFosB expression was observed well before the detection of morphologic change in both the lens and the retina. Within the lens, DeltaFosB expression was found in both the epithelium and fibers. The development of cataracts was a direct consequence of DeltaFosB expression and was not due to the disruption of an endogenous gene by transgene integration since cataracts could be prevented by silencing expression of DeltaFosB by feeding bitransgenic animals doxycycline (Dox). Moreover, cataracts were observed in bitransgenic mice derived from two independent TetOp-DeltaFosB founder lines but not in single NSE-tTA transgenic controls. Cataractogenesis was not a consequence of abnormal development, because mice conceived and raised on Dox to prevent expression of DeltaFosB also were subject to formation of PSC when expression of DeltaFosB was turned on in adult animals by removing Dox. Examination of biochemical parameters indicated that the earliest change observed was the disruption of calcium homeostasis with a significant increase in Ca(2+) influx, followed by a gradual but marked decrease in protein content. Significant changes in certain metabolic parameters and protein composition were also observed.

CONCLUSIONS

The DeltaFosB-induced cataract in which the major morphologic early event was the disruption of normal posterior fiber formation, may be a good model for PSC. By identifying DeltaFosB-regulated target genes, it should be possible to achieve a better understanding of the molecular mechanisms through which PSC is formed.

Effects of experimentally induced ametropia on the morphology and optical quality of the avian crystalline lens

PURPOSE

To examine the effects of refractive error on avian lens morphology and optical quality.

METHODS

Hatchling white leghorn chicks were unilaterally goggled for 7 days with either a form-deprivation goggle (n = 12), a -10 D defocus goggle (n = 12), or a +10 D defocus goggle (n = 12) to induce myopia and hyperopia. Optical quality of lenses (focal length and focal length variability) from treated and contralateral control eyes was assessed using a scanning laser apparatus. Lens morphology was examined by light and electron microscopy.

RESULTS

Although the induction of refractive errors did not significantly alter lens size, shape, paraxial focal length, or average focal length, average focal length variability increased. Lenses from eyes goggled with form-deprivation and +10 D defocus goggles demonstrated a twofold increase in average focal length variability, when compared with their contralateral controls. The morphology of the lens is not altered by these experimental manipulations.

CONCLUSIONS

This study provides evidence that the refractive development of the chick lens is not independent of the refractive development of the ocular globe and that chick lenticular development is influenced by both genetics and visual experience.

The relationship between rabbit lens optical quality and sutural anatomy after vitrectomy

This study was conducted first, to characterize structural changes in rabbit lenses after vitrectomy; and second, to assess whether such changes correlate with a quantifiable compromise in optical function. Unilateral, partial vitrectomies were performed on 2.5 month old Dutch Belted rabbits (n = 64). Age matched non-operated rabbits (n = 32) were used as controls. Lenses were analysed by correlative structural (light, scanning electron microscopic and three-dimensional computer-assisted drawings) and optical (low power helium-neon laser scan) analysis at 1.5, 3, 6 and 12 months post-surgery (n = 16 lenses from operated animals and n = 8 lenses from non-operated controls at each time point). Results demonstrate that in rabbits lens growth, or fiber formation, is compromised after vitrectomy. From 1.5 to 12 months after surgery, lenses had progressively more crooked posterior line sutures with sub-branches of increasing size and number in successive growth shells. Quantification of lens optical quality specifically along and/or between these atypical suture branches and sub-branches revealed a significant increase in focal length variability (sharpness of focus) after vitrectomy. A peripheral zone of fibers with abnormal posterior ends was produced surrounding the pre-surgical lens mass. This additional zone of aberrant fibers was associated with a quantifiable degradation in lens optics. Studies on the prevention of post-vitrectomy lens changes in this rabbit model may yield useful information applicable to the human condition.

Noncontact specular microscopy of human lens epithelium

PURPOSE

To obtain in vivo specular images of human lens epithelial cells (LECs) from persons with or without age-related cataract (ARC); to identify features that describe individual aspects of these complex images; to develop feature scales to quantify the severity of each feature; and to study the association of these features with LEC count, age, Lens Opacity Classification System III (LOCS III) classifications and microscopic features of lens epithelium in ARC.

METHODS

One hundred fifty-two individuals underwent ophthalmic examinations and LOCS III cataract classifications. Specular images of lenses were captured using a modified noncontact corneal specular microscope (SML-2; Konan, Hyogo, Japan). Enhanced images were graded in a masked fashion, and the presence or absence and severity of each of four features in the specular image ("columnar organization," "linear furrows," "puffy clouds," and "black holes") was graded on a four-step scale. The generalized linear model with intraclass correlation was used to ascertain the statistical significance of associations between age, sex, LOCS III grade, cell count, and feature grade. Capsulorrhexis specimens from 29 patients were studied with correlative light and electron microscopy.

RESULTS

LEC density declined with age and was inversely correlated with the scalar grade for puffy clouds and for the size and number of black holes. The scalar grade for columnar organization was inversely associated with the severity of posterior subcapsular and nuclear cataracts, which was the only feature associated with the LOCS III grade of ARC. No statistically significant associations were found between average cell count and LOCS III grade.

CONCLUSIONS

With the use of the corneal specular microscope excellent in vivo specular images of the LECs were obtained, the features in these images that correlated well with microscopic findings were classified, and cell density in vivo was estimated.

Effect of age on the morphology and optical quality of the avian crystalline lens

The effect of age on the avian lens was examined using White Leghorn chickens of five age groups: hatchling (n =19), 7 day (n = 15), 34 week (n =10), 2 year (n =24), and 5 year (n =25). The chick lens grows steadily up to 34 weeks of age, after which, the rate of growth slows down. During growth, average focal length of the lens becomes longer. However, no significant changes were noted between 2 and 5 year old lenses. An age related increase in average lenticular focal length variability (FLV) was observed, revealing that the optical quality of the lens decreases with age. Scanning electron microscopy demonstrated that: (1) the suture region of the lens becomes more diffuse and less precise with age; (2) the central regions of younger lenses are oblate spheroids, while older lenses become more apple-shaped; (3) individual lens fibres in the young lens are crescent-shaped, while older lens fibres are square-bracket-like in shape; (4) the edges of individual lens fibres become more jagged and irregular with age; and (5) the layering of lens fibres is more disorderly in older lenses, in contrast to the parallel and organized layering of fibres in young lenses.

A transgenic animal model of osmotic cataract. Part 1: over-expression of bovine Na+/myo-inositol cotransporter in lens fibers

PURPOSE

Intracellular osmotic stress is believed to be linked to the advancement of diabetic cataract. Although the accumulation of organic osmolytes (myo-inositol, sorbitol, taurine) is thought to protect the lens by maintaining osmotic homeostasis, the physiologic implication of osmotic imbalance (i.e., hyperosmotic stress caused by intracellular over-accumulation of organic osmolytes) on diabetic cataract formation is not clearly understood. Studies from this laboratory have identified several osmotic compensatory mechanisms thought to afford the lens epithelium, but not the lens fibers, protection from water stress during intervals of osmotic crisis. This model is founded on the supposition that the fibers of the lens are comparatively more susceptible to damage by osmotic insult than is the lens epithelium. To test this premise, several transgenic mouse lines were developed that over-express the bovine sodium/myo-inositol cotransporter (bSMIT) gene in lens fiber cells.

METHODS

Of the several transgenic mouse lines generated, two, MLR14 and MLR21, were analyzed in detail. Transgenic mRNA expression was analyzed in adult and embryonic transgenic mice by a coupled reverse transcriptase-polymerase chain reaction (RT-PCR) and in situ hybridization on embryonic tissue sections, respectively. Intralenticular myo-inositol content from individual mouse lenses was quantified by anion exchange chromatography and pulsed electrochemical detection. Ocular histology of embryonic day 15.5 (E15.5) embryos from both transgenic (TG) families was analyzed and compared to their respective nontransgenic (NTG) littermates.

RESULTS

Both RT-PCR and in situ hybridization determined that transgene expression was higher in line MLR21 than in line MLR14. Consistent with this, intralenticular myo-inositol from MLR21 TG mice was markedly higher compared with NTG littermates or MLR14 TG mice. Histologic analysis of E15.5 MLR21 TG embryos disclosed a marked swelling in the differentiating fibers of the bow region and subcapsular fibers of the central zone, whereas the lens epithelium appeared morphologically normal. The lenticular changes, initiated early during lens development in TG MLR21 embryos, result in severe bilateral nuclear cataracts readily observable in neonates under normal rearing and dietary conditions. In contrast, TG MLR14 pups reared under standard conditions produced no lens opacity.

CONCLUSIONS

Lens fiber swelling and related cataractous outgrowth positively correlated to the degree of lens bSMIT gene expression and intralenticular myo-inositol content. The affected (i.e., swollen) lens fibers appeared to be unable to cope with the water stress generated by the transgene-induced over-accumulation of myo-inositol and, as a result of this inability to osmoregulate, suffered osmotic damage due to water influx.

The internalization of posterior subcapsular cataracts (PSCs) in Royal College of Surgeons (RCS) rats. I. Morphological characterization

PURPOSE

To document lens ultrastructure during and after internalization of posterior subcapsular cataracts (PSCs) in Royal College of Surgeons (RCS) rats, a model for human autosomal retinal degenerative disease.

METHODS

RCS rat lenses at 2, 2.5, 3, 4, 6, 9, 12, and 15 months old were enucleated and fixed. For light and transmission electron microscopy (TEM), lenses were embedded in epoxy and sectioned along the visual axis. For scanning electron microscopy, lenses were dissected to expose the posterior fibers in concentric growth shells down to the internalized PSC plaques.

RESULTS

Overgrowth of the plaque began between 8 and 9 weeks postnatal and proceeded from the periphery to the posterior pole. This is in contrast to PSC formation which begins centrally and enlarges radially between 4-6 weeks postnatal. Peripheral-to-central overgrowth resulted in the formation of a convexo-concave, disk-shaped suture plane oriented parallel to the capsule. The initial fibers overlying the plaque were extremely flattened at their posterior ends. However, by 3 months postnatal, fiber ultrastructure was relatively normal and displayed only minor morphological irregularities. These temporal and structural changes were used to create 3-dimensional computer assisted-drawing (3D-CAD) reconstructions and animations. TEM examination of plaques revealed scattered fiber defects such as membrane whorls, globular aggregates and intracellular voids in both the internalized plaques and the initial overgrowth. The internalized PSC plaques had comparable morphology in all animals, regardless of age. Specifically, the posterior segments of fibers were enlarged and curved abnormally toward the capsule.

CONCLUSIONS

PSC plaques are not internalized and broken down in the classical cell biological sense (i. e. via lysosomal degradation). Rather the plaques retain their structure indefinitely as lens growth proceeds (albeit not entirely normally). This demonstrates that the lens has a restricted ability to respond to growth defects and effect a limited recovery after PSC formation.

The internalization of posterior subcapsular cataracts (PSCs) in Royal College of Surgeons (RCS) rats. II. The inter-relationship of optical quality and structure as a function of age

PURPOSE

The Royal College of Surgeons (RCS) rat is an animal model for human retinal degenerative disease and posterior subcapsular cataracts (PSCs). The purpose of this study was to correlate the structure and optical quality of RCS lenses with PSCs as a function of their internalization, with normal, non-cataractous, age-matched control lenses.

METHODS

Correlative light (LM), scanning electron microscopic (SEM), three-dimensional computer assisted drawings (3D-CADs) and low power helium-neon laser scan analysis were used to examine the structure and function of lenses.

RESULTS

The optical properties (average focal length variability; sharpness of focus) of RCS rat lenses are quantitatively compromised by PSCs. Correlative LM and SEM analysis of RCS lenses at various stages of PSC internalization (1.5, 3, 6, 9, 12 and 15 months of age), revealed that the sutures formed by additional fiber growth were progressively more abnormal. During PSC internalization, two to nine small suture branches were formed and arranged in modified line to multiple y configurations rather than the normal three branch y sutures. These temporal changes were also chronicled in animated 3D-CAD videos derived from lens reconstructions based on LM and SEM micrographs from the selected time points stated above. However, laser scan analysis also revealed that as the PSCs of RCS rat lenses were progressively internalized, there was a steady improvement in total sharpness of focus that reached normal levels by 12 months of age. The correlation of laser scan and structural data from specific regions of lenses revealed the following: 1. The abnormal posterior sutures of RCS rats with internalized PSCs effect a greater reduction in optical quality than normal posterior sutures of age-matched controls; 2. However, the resulting abnormal suture plane area was cumulatively similar to that of age-matched controls; 3. Thus, total optical quality was similar between RCS lenses with internalized PSCs and age-matched controls by 12 months of age.

CONCLUSIONS

The results of this study show that RCS lenses with internalized PSCs can appear grossly, and indeed optically perform, at levels comparable to aged lenses. These findings are consistent with clinical observations of spontaneous recovery from PSC. The results suggest that human PSCs that occur as a consequence of retinal degenerative disease could also be the result of abnormal posterior suture growth. If this is proven to be the case, such PSCs may have some capacity for repair or recovery thereby obviating their surgical removal.

Anterior polar cataracts in CS rats: a predictor of mature cataract formation

PURPOSE

The objective of this study was to characterize the morphology of the anterior opacities formed during recovery from posterior subcapsular cataract (PSC) in Royal College of Surgeons (RCS) rats.

METHODS

Lenses from RCS rats at 8 and 12 weeks postnatal (n = 14 and 12, respectively) were examined under a dissecting microscope for the presence of anterior opacities. Lenses with anterior opacities were fixed, embedded in epoxy resin, and sectioned along the optic axis for light microscopy (LM) and transmission electron microscopy (TEM).

RESULTS

At eight weeks postnatal, 21.5% of animals (3/14) had anterior cataracts. Light microscopy of 1- to 2-microm-thick sections revealed an anomalous layer of material located at the epithelium-fiber interface, which was identified as a zone of liquefaction by TEM. Epithelial cells had minor structural defects but were not necrotic. Anterior portions of elongating and cortical fibers under the zone of liquefaction were undisrupted, whereas their posterior portions had numerous vacuoles. The anterior opacities were classified as anterior polar cataracts (APCs) based on the location and type of morphologic damage in the affected lenses. At twelve weeks postnatal, 25% of animals (3/12) had APCs that involved prominent vesiculation of the anterior cortex. Ultrastructural examination showed that large vesicles were located between and inside anterior fibers and that most extracellular spaces were abnormally widened. Posteriorly, internalization of the PSC by new fiber growth was disordered and displayed vesiculation and density variations. In the bow region, LM revealed minor structural irregularities that were identified as groups of apparently degenerating fibers by TEM.

CONCLUSIONS

APCs in RCS rats are caused by degeneration of elongating fibers in the bow region and subsequent damage in the superficial anterior cortex. The percentage of animals with APCs (25%) was consistent with the percentage of animals in which mature cataracts eventually develop. The morphologic changes, time of onset, and percentage of animals affected suggest that APC is the initial manifestation of mature cataract formation in RCS rats.

The effect of photochemical stress upon the lenses of normal and glutathione peroxidase-1 knockout mice

This communication investigates the effect of oxidative stress upon the lenses of young normal and glutathione peroxidase-1 (GSHPx-1) Knockout mice. Both normal and knockout lenses have similar biochemical and morpholigical characteristics and the elimination of GSHPx-1 only decreases slightly the ability of the lens to degrade H2O2. Examination of the effect of a 4 hr photochemical stress on morphological characteristics indicates that there is comparable damage in the normal and knockout lenses in the epithelial and bow regions while the posterior region remains normal. However, at 24 hrs post-insult, the normal lenses appear to recover somewhat in the bow region while the knockout bow and posterior regions have extensive damage. In contrast to the morphological data, the biochemical parameters (14C)choline transport and (3H)thymidine incorporation are affected to a somewhat greater extent in the knockout lenses than in normal lenses. While both of these parameters are further affected in the 24 hr post-insult period, there is no further change in the relative effects upon normal and knockout lenses. Non-protein thiol is affected in a similar manner in both lens types. The effect upon biochemical parameters of tertiary butyl hydroperoxide (TBHP) insult was similar to H2O2 and photochemical stress. The overall conclusion is that young GSHPx-1 knockout lenses handle oxidative stress somewhat less effectively than comparable normal lenses but non-stressed knockout lenses appear normal. These results differ from observations reported by Reddy et al. (1997) under somewhat different conditions.

The structure of posterior subcapsular cataracts in the Royal College of Surgeons (RCS) rats

The Royal College of Surgeons (RCS) rat is an animal model for human autosomal recessive retinitis pigmentosa. As the retinas of these animals degenerate from two to six weeks after birth, posterior subcapsular cataracts (PSCs) develop, presumably in response to toxic lipid peroxides formed by degenerating rod outer segments. Morphologically, these PSCs are thought to be characterized by a proliferation of dysplastic bladder-like fibers, or Wedl cells, in the meridional region of the lens, that subsequently migrate to, and aggregate at, the posterior pole as the PSC. This report presents the results of correlative scanning (SEM) and transmission (TEM) electron microscopic as well as light microscopic (LM) analysis of the ultrastructure of RCS PSCs. SEM analysis of two, four and six week old lenses (n=6-10 specimens per age group) demonstrated that the PSCs of RCS rats resulted from a growth malformation of the posterior fiber ends from four to six weeks. The PSC is composed of markedly enlarged and irregular posterior fiber ends aberrantly curved away from the polar axis toward the vitreous rather than overlapping and abutting to form suture branches within and between concentric growth shells. LM analysis revealed evidence of progressively more numerous, enlarged, and irregular, ovate cellular profiles at the posterior pole from four to six weeks. However, there was no evidence of Wedl cells either within the meridional row region or along a migratory path from the equator to the posterior pole at any age. TEM analysis confirmed that the size and abnormal shapes of cellular profiles were consistent with SEM analysis and that nuclei were never observed within the plaque. In addition, there was considerable variation in cytoplasmic densities between cells. Also, dense deposits were frequently noted between cells and beneath the capsule. The orientation of posterior fiber end profiles to the posterior capsule was 45, 70 and 90 degrees at respectively two, four and six weeks of age. These results show that RCS PSCs are a consequence of abnormal posterior fiber end growth culminating in a posterior opacity.

Morphology of the normal human lens

PURPOSE

To provide a quantitative, morphologic description of differentiated lens fiber cells in all regions of aged normal human lenses.

METHODS

Transparent normal human lenses (age range, 44 to 71 years) were examined with correlative transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Vibratome sections allowed examination of internal structures, whereas dissected whole lenses revealed surface characteristics. Additionally, image analysis was used to measure cross-sectional areas of fiber cells.

RESULTS

Approximate regional dimensions (percentage of diameter and thickness, respectively) were determined for whole lenses: cortex 16%, 17%; adult nucleus 24%, 21%; juvenile nucleus 12%, 9%; fetal nucleus 45%, 49%; and embryonic nucleus 3%, 4%. Cortical cells were irregularly hexagonal, and the average cross-sectional area measured 24 +/- 9 microns2. Adult nuclear cells were flattened with intricate membranous interdigitations and an area of 7 +/- 2 microns2. Juvenile nuclear cells had an area of 14 +/- 5 microns2. Fetal nuclear cells were rounded with an area of 35 +/- 22 microns2. Embryonic nuclear cells also were rounded and had a variable area of 80 +/- 68 microns2. Fiber cell cytoplasm in all lens regions appeared smooth in texture and homogeneous in staining density.

CONCLUSIONS

Both TEM and SEM are necessary to obtain a complete description of fiber cells. Cross-sections of fibers give new insights into the lamellar organization of the lens, indicating that each region has characteristic cell shapes and sizes. Furthermore, average dimensions were used to demonstrate that the number of cells and approximate growth rates vary significantly between adjacent regions.

An ultrastructural analysis of the epithelial-fiber interface (EFI) in primate lenses

The purpose of this study was to conduct a comprehensive ultrastructural analysis of the epithelial-fiber interface (EFI) in normal adult primate (Macaque nemestrina and fascicularis; 6-9 years old, n = 10) lenses. Scanning electron microscopy (SEM) was used to initially characterize the gross size, shape and three-dimensional organization of central zone (cz) epithelial cells and the anterior ends of elongating fibers beneath these cells. This fiducial information was essential to properly orient lens pieces in freeze fracture specimen carriers for the production of replicas with unambiguously identifiable EFI. Transmission electron microscopy (TEM) of replicas and thin-sectioned material were used to ultrastructurally analyse the cz EFI. TEM thin-sectioned material was also used to ultrastructurally analyse the pregerminative (pgz), germinative (gz) and transitional zone (tz) EFI. Correlative SEM and TEM of cz EFI components revealed that the apical membrane of both epithelial and elongating fiber cells were irregularly polygonal in shape, and aligned in parallel as smooth, concave-convex surfaces. However, whereas epithelial cell apical surfaces had minimal size variation, elongating fibers were larger and considerably variable in size. Quantitative analysis of > 10000 micron2 cz elongating fiber apical surfaces failed to detect any gap junctions defined in freeze fracture replicas as complementary aggregates of transmembrane proteins (connexons) conjoined across a narrowed extracellular space. However, a comparable frequency of vesicular events was noted in this region as quantified previously in adult and embryonic chick lens. Correlative TEM analysis > 1500 linear micrometers of thin-sectioned EFI from this region confirmed the presence of epithelial-epithelial gap junctions, elongating fiber-elongating fiber gap junctions, and an extreme paucity of epithelial-elongating fiber gap junctions. In contrast, TEM analysis of > 1000 linear micrometers of thin-sectioned pgz, gz and tz EFI, confirmed the presence of epithelial-epithelial gap junctions, elongating fiber-elongating fiber gap junctions, numerous epithelial-elongating fiber adherens junctions and a few epithelial-elongating fiber gap junctions. Thus, the results of this and previous quantitative morphological and physiological studies (electronic and dye coupling) demonstrate that there is limited coupling between cz epithelial cells and underlying elongating fibers. Furthermore, the absence of gap junctional plaques in cz EFI freeze-fracture replicas and either pentalaminar or septalaminar profiles in correlative thin-sections, suggests that this limited coupling could be mediated via isolated gap junction channels. However, the results of this and previous quantitative studies further show that a greater degree of coupling exists across the pgz, gz and tz regions of the EFI and that this coupling is likely to be mediated by gap junction plaques. Finally, this and other studies continue to demonstrate that transcytotic processes play a role in lens physiology at the EFI.

Calcimycin-induced lens epithelial cell apoptosis contributes to cataract formation

Previous studies have shown that calcimycin induces cataract in organ culture. To investigate the mechanism of this induction, the viability of lens epithelial cells in calcimycin (calcium ionophore, A23187)-treated rat lenses were examined. During incubation of lenses with 5 microM calcimycin, apoptotic epithelial cells were found after a 2-hr treatment as determined by terminal deoxynucleotidyl transferase (TdT) labeling. The percentage of apoptotic cells quickly rose as the incubation time increased. After a 12-hr incubation, more than 60% of the lens epithelial cells underwent apoptosis. Prolonged c-fos expression, previously shown to be an indicator of programmed cell death, was also observed during this treatment. DNA fragmentation assays further confirmed that the TdT labeled cells were indeed apoptotic. Under the same incubation conditions, the cultured lenses gradually lost transparency and became completely opaque in about 30 hr. Since the vertebrate lens contains only a single layer of epithelial cells, apoptotic death of these cells activated by calcimycin quickly destroys the lens epithelium, impairs homeostasis of the underlying fiber cells and initiates development of lens opacification.

Lens epithelial cell apoptosis appears to be a common cellular basis for non-congenital cataract development in humans and animals

Cataract is a major ocular disease that causes blindness in many developing countries of the world. It is well established that various factors such as oxidative stress, UV, and other toxic agents can induce both in vivo and in vitro cataract formation. However, a common cellular basis for this induction has not been previously recognized. The present study of lens epithelial cell viability suggests such a general mechanism. When lens epithelial cells from a group of 20 cataract patients 12 to 94 years old were analyzed by terminal deoxynucleotidyl transferase (TdT) labeling and DNA fragmentation assays, it was found that all of these patients had apoptotic epithelial cells ranging from 4.4 to 41.8%. By contrast, in eight normal human lenses of comparable age, very few apoptotic epithelial cells were observed. We suggest that cataract patients may have deficient defense systems against factors such as oxidative stress and UV at the onset of the disease. Such stress can trigger lens epithelial cell apoptosis that then may initiate cataract development. To test this hypothesis, it is also demonstrated here that hydrogen peroxide at concentrations previously found in some cataract patients induces both lens epithelial cell apoptosis and cortical opacity. Moreover, the temporal and spatial distribution of induced apoptotic lens epithelial cells precedes development of lens opacification. These results suggest that lens epithelial cell apoptosis may be a common cellular basis for initiation of noncongenital cataract formation.

A brief photochemically induced oxidative insult causes irreversible lens damage and cataract. I. Transparency and epithelial cell layer

Short-term photochemical insult of cultured rat lenses caused by the generation of H2O2, O2<--and OH. was found to lead to rapid irreversible damage to the epithelial cell layer. This irreversible damage was measured by Trypan blue staining, terminal deoxyribonucleotidyl transferase labeling, DNA laddering and morphological analyses. There appears to be an inverse relationship between the period of photochemical insult and the post-insult time required to observe epithelial cell damage. Insulting periods of a few hours require post-insult intervals of days to observe significant cell damage and weeks before complete cortical cataracts are found. Epithelial cell damage precedes the loss of transparency.

The ultrastructure of epithelial and fiber cells in the crystalline lens

Crystalline lenses are often simply described as inside-out stratified epithelial-like organs composed of uniform (hexagonal cross-section profiles) crescent-like cells, arranged end-to-end in concentric shells around a polar axis. In this manner, as light is transmitted through lenses, their highly ordered architecture contributes to transparency by effectively transforming the multicellular organ into a series of coaxial refractive surfaces. This review will attempt to demonstrate that such a description seriously understates the structural complexity that produces lenses of variable optical quality in different species as a function of development, growth, and age. Embryological development of the lens occurs in a similar manner in all species. However, the growth patterns and effects of aging on lens fibers varies significantly among species. The terminally differentiated fiber cells of all lenses are generally hexagonal in cross section and crescent shaped along their length. But, while the fibers of all lenses are arranged in both highly ordered radial cell columns and concentric growth shells, only avian lens fibers are meridian-like, extending from pole to pole. In all other species, two types of fibers defined by different shapes are continuously formed throughout life. The majority of fibers are s-shaped, with ends that do not extend to the poles. Rather, the ends of these fibers are arranged as latitudinal arc lengths within and between growth shells. The overlap of the ends of specifically defined groups of such fibers constitutes the lens suture branches. The location, number, and extent of suture branches within and between growth shells are important considerations in lens function because the shapes of fiber ends, unlike that along fiber length, are very irregular. Consequently, as light is transmitted through sutures, spherical aberration (i.e., focal length variation) is increased. The degree of focal length variability depends on the arrangement of suture branches within and between growth shells, and this architecture varies significantly between species. The lifelong production of additional fibers at the circumference of the lens, culminating in new growth shells, neither proceeds equally around the lens equator, nor features identical fibers formed around the equator. Suture formation commences in the inferonasal quadrant, and continues sequentially in the superotemporal, inferotemporal, and finally the superonasal quadrants. During this process, lens growth produces fibers of specifically defined length and shape as a function of their equatorial location.(ABSTRACT TRUNCATED AT 250 WORDS)

The interrelationship of lens anatomy and optical quality. II. Primate lenses

We have quantified the influence of lens sutural anatomy on optical quality (focal length variability, i.e. spherical aberration) in adult monkeys (Macaque nemestrina). Adult lenses (n = 6) were initially scanned by a low-power helium-neon laser beam that was passed at a series of acute angles to, and/or directly through, lens sutures. Optical analysis showed that while the 'star' sutures of primate lenses exerted a quantifiable negative effect on focal length variability, this detrimental effect was far less significant than that attributable to 'line' and 'Y' sutures in non-primate lenses. Correlative morphological and 3-D computer-assisted drawing (CAD) analysis of the laser-scanned lenses areas, as well as of variably aged lenses (n = 30), revealed that primates have a more complex lens architecture than non-primates. Non-primate lenses feature suture planes, aligned along the visual axis that are responsible for a significant quantifiable increase in spherical aberration. Primate lenses are characterized by an absence of continuous suture planes aligned along the visual axis. Rather, 3-D-CADs of primate lenses demonstrate that distinct generations of progressively more complex sutures are produced as a function of development, growth, and age. In succession, 'Y' sutures (three branches) are formed throughout embryonic development, 'simple star' sutures (three-six branches) evolve after birth and through infancy, 'star' sutures (six-nine branches) are made in young adult lenses and, finally, 'complex star' sutures (nine-15 branches) are laid down from middle through old age. In view of the fact that slit-lamp evaluation of cataractous lenses often reveals abnormally thin zones of discontinuity, it is significant to note that the temporal development of the zones of discontinuity in normal human lenses is essentially identical to the progressive iteration of offset monkey lens sutures. In conclusion, these studies describe a specific structural aspect of lenses that adversely influences optical quality, and relates it to the most commonly employed clinical technique to identify and monitor the progress of cataracts.

The zones of discontinuity in the human lens: development and distribution with age

Statistical analysis of Scheimpflug images from the crystalline lenses of 100 emmetropic human subjects ranging in age from 18 to 70 yr confirms that specific zones of discontinuity are a function of lens development and growth. At and beyond the age of 40 yr, as many as four sharply demarcated and complementary zones are seen within the anterior and posterior lens cortex. The locations of the inner edges of the anterior cortical zones of discontinuity were characterized relative to the central sulcus of the lens. Consecutively from the central sulcus, the distances were 1.094, 1.415, 1.695, and 1.994 (+/- 0.11 mm). Since nuclear thickness in the adult lens is age-independent and the rate of cortical growth has been characterized, the location of the inner margins of the zones are indicative of the age at which they originated; these ages were 4 (+/- 1 yr), 9 (+/- 2 yr), 19 (+/- 4yr), and 46 (+/- 10 yr). All of the zones become broader along the outer margin and more dense upon aging, with specific zones appearing to merge in older presbyopic lenses. While lens fetal nuclear transparency decreases with age, it does not feature zones of discontinuity; instead, symmetrically amorphous regions appear centrally in the anterior and posterior nucleus. This demonstration of the onset of specific zones of discontinuity in emmetropic individuals, at defined periods of lens growth that are synchronous the production of successively more complex lens sutures, strongly suggests a causal relationship between lens sutures and the zones of discontinuity.

The interrelationship of lens anatomy and optical quality. I. Non-primate lenses

We have quantified the influence of 'Y' sutures on lens optical quality (spherical aberration, i.e. focal length variability) as a function of age. Young (n = 6) and old (group 1, n = 5; and group 2, n = 4) bovine lenses were initially scanned by a low-power (2 mW) helium-neon laser beam passed either through or at a series of acute angles to suture branches. In all lenses, focal length variability was least when the beam was passed through areas of the lens devoid of sutures and greatest when passed through sutures. In older lenses, variability was also significantly increased in all locations though to a greater degree at sutures. Correlative morphological analysis by scanning electron microscopic (SEM) and three dimensional (3-D) computer-assisted drawings (CADs) revealed the following: (1) young lenses had uniformly hexagonal fibers arranged in parallel radial cell columns (RCCs), while old lenses had nonuniformly hexagonal fibers arranged in variably parallel RCCs; (2) the irregularly-sized and -shaped ends of young fibers overlapped within growth shells to form complementary anterior and posterior symmetrical 'Y' suture patterns, while larger and more irregularly-shaped ends of older lenses overlapped to form asymmetrical 'Y' patterns; and (3) the identical suture patterns in successive shells of young lenses resulted in inverted triangular suture planes extending from the embryonic nucleus to the lens periphery, while the progressively wider and more serpentine suture branches of old lenses resulted in inverted pyramidal suture planes with narrow apices oriented towards the embryonic nucleus and broad irregular bases oriented toward the lens periphery. Thus, there is a significant interrelationship between lens optical quality and structure that varies as a function of age. These results extend and confirm the results of our earlier studies on lenses with simpler 'line' sutures and preface our studies of primate lenses with more complex 'star' sutures. All of these studies show that lens sutural anatomy should be considered when evaluating the optical quality of normal and pathological lenses.

Intercellular communication between epithelial and fiber cells of the eye lens

Results of electrical, dye-coupling and morphological studies have previously suggested that gap junctions mediate communication between the anterior epithelium of the lens and the underlying lens fiber cells. This connection is believed to permit ‘metabolic cooperation’ between these dissimilar cell types and may be of particular importance to the fiber cells, which are thought incapable of autonomous ionic homeostasis. We reinvestigated the nature of the connection between epithelial and fiber cells of the embryonic chicken lens using fluorescence confocal microscopy and freeze-fracture analysis. In contrast to earlier studies, our data provided no support for gap-junction-mediated transport from the lens epithelium to the fibers. Fluorescent dyes loaded biochemically into the lens epithelium were retained there for more than one hour. There was a decrease in epithelial fluorescence over this period, but this was not accompanied by an increase in fiber cell fluorescence. Diffusional modeling suggested that these data were inconsistent with the presence of extensive epithelium-fiber cell coupling, even if the observed decrease in epithelial fluorescence was attributed exclusively to the diffusion of dye into the fiber mass via gap junctions. Furthermore, the rate of loss of fluorescence from isolated epithelia was indistinguishable from that measured in whole lenses, suggesting that decreased epithelial fluorescence resulted from photobleaching and leakage of dye rather than diffusion, via gap junctions, into the fibers. Analysis of freeze-fracture replicas of plasma membranes at the epithelial-fiber cell interface failed to reveal evidence of gap-junction plaques, although evidence of endocytosis was abundant. These studies were done under conditions where the location of the fracture plane was unambiguous and where gap junctions could be observed in the lateral membranes of neighboring epithelial and fiber cells. Paradoxically, tracer molecules injected into the fiber mass were able to pass into the epithelium via a pathway that was not blocked by incubation at 4 degrees C or by treatment with octanol and which excluded large (approximately 10 kDa) molecular mass tracers. Together with previous measurements of electrical coupling between fiber cells and epithelial cells, these data indicate the presence of a low-resistance pathway connecting these cell types that is not mediated by classical gap junctions.

Cations, oxidants, light as causative agents in senile cataracts

Lens transparency is a function of regular cell shape, regular cell volume, minimal extracellular space, and minimal scatter elements. The cellular structure and molecular structure of the lens is reviewed. The importance of the cytoarchitecture especially the sutures, is discussed. The high cholesterol: phospholipid ratio of the lens fiber cell membranes is related to the functions of low permeability, low fluidity, and mechanical stability. Also reviewed are the contributions of the lens crystallins to lens clarity and to lens refractive index. The importance of intracellular and extracellular cation and water concentrations are reviewed. Finally the effects of systemic diseases, oxidation, and light on lens clarity are discussed relative to changes in lens fiber cell cation concentrations.

Lens optical quality is a direct function of lens sutural architecture

We analyzed the structural and functional relationship between lens sutures and lens optical quality (focal length variability) by correlative scanning electron microscopy (SEM) and laser scan analysis. Twenty-two rabbit lenses (8 pigmented and 14 albino) were used in this study. Lenses were initially scanned by a low-power helium-neon laser beam that was passed either at an acute angle to a lens suture or along a lens suture. The results of laser scan analysis with the incident beam passed at an acute angle to a lens suture showed that generally, rabbit lenses were well corrected for spherical aberration. Subsequent SEM analysis showed that areas of lenses scanned that produced the least amount of focal variability were characterized by uniform fiber cells arranged in parallel, radial cell columns. In contrast, the results of laser scan analysis with the incident beam passed along a lens suture showed that there was significant focal length variability, i.e., spherical aberration at the lens sutures. Subsequent SEM analysis showed that the areas of lenses scanned that produced the greatest amounts of focal variability (lens sutures) were characterized by nonuniform fiber cell ends arranged as erratic suture branches in single growth shells and collectively as erratic suture planes formed between growth shells extending from the embryonic nucleus to the lens periphery. Furthermore, the amount of focal variability was directly proportional to the degree of structural disorder at the lens sutures. This is the first study to unequivocally show that the relationship between lens optical quality and specific parameters of lens morphology (lens sutures) can be quantified. These findings may help to elucidate the pathologic changes that lead to presbyopia and cortical cataractogenesis because these lenses are characterized by asymmetrical suture patterns and planes.

Relationship of the expression of the multidrug resistance gene product (P-glycoprotein) in human colon carcinoma to local tumor aggressiveness and lymph node metastasis

P-glycoprotein mediates classic multidrug resistance by functioning as an efflux pump that excretes lipophilic chemotherapeutic drugs from cancer cells. We now report an association of P-glycoprotein in colon carcinomas with another tumor property, i.e., enhancement of local tumor aggressiveness. P-glycoprotein was detected with monoclonal antibody immunohistochemistry in 65 of 95 primary colon adenocarcinomas, which were stage B1 or greater. In all but 1 of the 95 cases, solitary invading carcinoma cells were present at the leading edge of the tumor. This subpopulation of invasive carcinoma cells expressed P-glycoprotein (P-Gp+) in 47 of the 95 surgically resected colon specimens. Cases were grouped on the basis of the presence (Group 1, 47 cases) or absence (Group 2, 48 cases) of P-Gp+ invasive carcinoma cells. There was a significantly greater incidence of vessel invasion (P less than 0.001) and lymph node metastases (P less than 0.01) in Group 1 cases. Groups 1 and 2 did not differ with respect to tumor size, depth of invasion of the bowel wall, histological grade, maximum tumor size, mitotic index, mucin production, or presence of perineural invasion (P greater than 0.1). Our findings indicate that P-Gp+ invasive colon cancer cells may have an increased potential for dissemination, suggesting that P-glycoprotein may influence cell behavior.

Ultrastructural, biochemical, and immunologic evidence of receptor-mediated endocytosis in the crystalline lens

The lens epithelium is essentially the basal layer of the crystalline lens of the eye, an uncommon stratified epithelium. Ions and metabolites present in the aqueous humor gain access to the lens epithelium by diffusion through the lens capsule (the basement membrane of the lens epithelium). Then, it is presumed, the underlying lens fiber cells obtain necessary ions, metabolites, and nutrients through gap junctions conjoining the apical surfaces of the lens epithelial cells from the basal layer with the apical surfaces of elongating fiber cells from upper strata. In this report, correlative morphologic, biochemical, and immunochemical evidence is presented that both lens epithelial and fiber cells use endocytotic and/or transcytotic processes rather than being solely dependent on gap junctions for metabolic cooperation. Freeze-fracture analysis of the apicoapical interface between lens epithelial and elongating fiber cells (epithelial-fiber cell interface [EFI]) revealed protrusions and pits of two distinct sizes (average diameters, 46 and 126 nm). Gap junctions with tight particle packing were only rarely observed at the EFI. Gap junctions with loose particle packing were never observed at the EFI. "Orthogonal arrays" of intramembrane particles (OAPs) were not uncommon at the EFI. Thin-sections taken perpendicular to the EFI confirmed the existence of micropinocytotic and clathrin-coated vesicles in both lens epithelial and elongating fiber cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of separate preparations of lens epithelial and fiber cells, specifically enriched for clathrin-coated vesicles, showed a 180-kD protein. Western blot analysis of this protein revealed selective cross-reactivity with polyclonal anticlathrin antibodies. These results strongly suggest that transcytotic processes provide a primary route for the entry and egress of macromolecules in the lens.

ABO blood type predicts the cytolocalization of anti-P-glycoprotein monoclonal antibody reactivity in human colon and ureter

Classic multidrug resistance is mediated by a P-glycoprotein. Using monoclonal antibody C219 (MAb C219) in an immunohistochemical study, we found high levels of putative Golgi P-glycoprotein in normal columnar and transitional epithelium in subpopulations of patients with specific blood types. For example, Golgi staining was present in blood type A patients in 46% of normal colon samples (N = 21) and 88% of normal ureter samples (N = 17). In comparison, Golgi staining was present in blood group O patients in only 6% of normal colon samples (N = 34) and in 0% of normal ureter samples (N = 19). The association of MAb C219 Golgi staining with blood type A and lack of Golgi staining with blood type O was statistically significant in normal colon (P = .001) and normal ureter (P less than .0001). Inappropriate hyperexpression of P-glycoprotein was frequently found in colon carcinomas. Additional evidence that Golgi MAb C219 reactivity represents P-glycoprotein is presented. This includes (1) immunostaining of Golgi with two anti-P-glycoprotein MAbs, C219 and JSB-1, and (2) experiments in which Mab C219 Golgi reactivity was blocked by preincubation of MAb C219 with a specific P-glycoprotein epitope-containing peptide. The high degree of association of Golgi P-glycoprotein with blood type A may suggest a role for P-glycoprotein in processing or trafficking of specific blood group antigens.

Measuring the volume fraction of bone ingrowth: a comparison of three techniques

The need for quick, accurate, and reproducible methods to measure the amount of bone within porous metals has increased as the use of these materials has become more common within orthopedics. The purpose of this paper is to compare measurements of bone ingrowth using microradiography, stained histology, and backscattered electron imaging-scanning electron microscopy (BEI-SEM) in cementless, porous-coated acetabular components retrieved from human patients. BEI-SEM of bone ingrowth into porous metal provided excellent images for quantitative analysis. The stained sections and BEI-SEM images provided very comparable results, while microradiography consistently underestimated the porosity of the porous coating and overestimated the amount of bone ingrowth.

P-glycoproteins in pathology: the multidrug resistance gene family in humans

Many cancers do not respond to chemotherapy on primary exposure to drugs, thus manifesting intrinsic drug resistance. Other cancers that do initially respond subsequently become resistant to the same drugs and simultaneously to other drugs to which the patient has had no previous exposure. This is a form of acquired drug resistance. There is a pressing need to better understand the mechanisms of drug resistance and to use this information to develop strategies for the chemosensitization of drug-resistant tumors. A goal of the pathology laboratory is to offer chemosensitivity tests that identify intrinsic or acquired resistance of tumors to specific drugs or classes of drugs to enable the clinician to tailor therapy to the biology of cancers in individual patients. Multidrug resistance is one type of drug resistance. It can be present in either an intrinsic or acquired form. The human gene that confers human multidrug resistance, the MDR1 gene, has been cloned and classified as a member of the MDR gene family. Its encoded protein, called Mdr1, is an energy-driven membrane efflux transporter that maintains intracellular concentrations of certain chemotherapeutic drugs at nontoxic levels. Useful model systems for studying multidrug resistance have been developed in several research laboratories. Applying selection pressure by exposing cultured cancer cells to escalating doses of natural product anti-cancer drugs allows cross-resistant cell lines to be produced which share patterns of drug resistance with human cancers. A common feature of these drug-resistant lines is the expression of Mdr1. Using techniques of genetic engineering, molecular probes have been developed that can be used to measure MDR1 mRNA and MDR1 gene amplification. Mdr can be measured by immunochemistry methods. Currently, such measurements are being used to stratify patients in clinical trials designed to determine if chemosensitization by inhibition of the pump function of Mdr is a clinically useful therapeutic strategy. If successful, Mdr/MDR1 mRNA laboratory testing might significantly increase the clinical laboratory's role in cancer patient management.

The ultrastructure of fiber cells in primate lenses: a model for studying membrane senescence

We have compared the surface morphology of the youngest (cortical) fiber cells with that of the most senescent (nuclear) fiber cells in monkey and baboon crystalline lenses by stereo scanning electron microscopy (SEM) and thick-section stereo transmission electron microscopy (TEM). Both the broad and the narrow faces of the most senescent fiber cells featured distinctive, polygonal areas (domains) of furrowed cell membrane. The domains ranged in size from 2.42 to 8.78 microns2. Stereopair SEM and TEM micrographs demonstrated precisely oriented microvilli measuring approximately 0.14 micron in diameter and ranging in length from 1.27 to 4.65 microns overlying each ridge in the domains. Formation of microvilli on senescent cells has been noted in other types of aging cells but they are imprecisely arranged and their function is unknown. Since every fiber cell remains in a fixed location (relative to other fiber cells) throughout life, the lens provides a unique model to study structure-function relationships of senescent microvilli in situ. The discovery of an age-related elaboration of numerous microvilli on senescent fiber cells of noncataractous lenses invalidates the currently accepted theory that close, parallel apposition of the broad faces of lens fiber cells is necessary for the lens to be transparent.

An ultrastructural analysis of plasma membrane in the U18666A cataract

Because the cholesterol concentration of lens fiber cell membrane in general and lens intercellular junctions in particular is comparatively high, it is likely that it plays a major role in maintaining these structures. In addition, the high concentration of cholesterol in fiber cell membrane is also likely to influence membrane fluidity. Subcutaneous injections of U18666A (3 beta-(2-diethylaminoethoxy) androst-5-en-17-one HCl) into rats effects: (1) a blockade of sterolgenesis in the lens; (2) a depletion of lens fiber cell membrane cholesterol; and (3) the development of irreversible nuclear cataracts. In the present study we have analyzed the ultrastructure of lens fiber cell membrane in adult rats, these by the freeze-etch technique. Whereas it has been previously demonstrated that intercellular junctions comprise approximately one-third of the intermediate cortical fiber cell membrane in adult rats, these junctions were completely absent between comparable fiber cells taken from opaque regions of the U18666A cataractous lenses. There was also a concomitant increase in the extracellular space between the opaque fiber cells and a substantial redistribution of intramembrane proteins in the exoplasmic and protoplasmic faces of these cells. These findings support a "hypothesis" that inhibition of endogenous lens cholesterol production leads to damage and/or degeneration of lens fiber cell membrane in general and in intercellular junctions in particular, resulting in the production of an irreversible nuclear cataract.

Ultrastructure of tight junctions in prostaglandin-exposed rat stomach

The effect of intragastric misoprostol, a synthetic prostaglandin E1 methyl ester analog, on the morphology of rat stomach was studied by transmission and scanning electron microscopy. Adult male Sprague-Dawley rats received misoprostol at dose levels ranging from 50 to 1000 micrograms/kg body weight and were sacrificed after 30 min. At all dose levels, normal organelle ultrastructure was maintained in epithelial cells on the surface, within gastric pits, and lining the gastric glands. Quantitative freeze-fracture electron microscopy was used to examine the influence of misoprostol on epithelial-cell tight junctions, major structural components of the mucosal barrier. The numbers of intramembrane fibrils and the depths of the tight-junction complexes did not differ significantly between controls and animals exposed to 1000 micrograms/kg misoprostol (P greater than 0.05). Therefore, alterations in gastric epithelial tight-junction ultrastructure do not appear to account for the cytoprotective effect of misoprostol.

Effects of XeCl excimer laser on the eyelid and anterior segment structures

We evaluated the in vitro and in vivo effects of an XeCl excimer laser on the eyelid and anterior segments of the eye. The wavelength of this laser was successfully transmitted through a quartz fiberoptic system. The action of the XeCl excimer laser through our system was more photocoagulative than photoablative.

Cell-to-cell fusion of lens fiber cells in situ: correlative light, scanning electron microscopic, and freeze-fracture studies

We have discovered cell-to-cell fusion between fiber cells of adult frog lenses in situ. Stereo scanning electron microscopy (SEM) revealed fusion between neighboring fiber cells in radial cell columns (RCCs) and in the same growth ring, respectively. Cell-to-cell fusion of fiber cells in the lens produced fusion zones that in cross-section were larger and of different polygonal shapes than unfused fiber cells. The shape and sizes of fiber cells surrounding fusion zones and the alignment of RCCs were also altered. Serial sectioning through fusion zones confirmed that they were areas of cell-to-cell continuity established by the union of neighboring fiber cells as seen by SEM. Fusion zones represent a previously unrecognized intercellular pathway in the adult frog lens. Although numerous fusion zones were seen throughout the lens cortex and nucleus, cell-to-cell fusion was rarely observed to have occurred between elongating fiber cells. Interestingly, communicating junctions with an unusual ultrastructure that closely resembles the appearance of membranes in the process of fusion demonstrated in other systems were frequently seen in the region of the superficial cortex where fusion zones were most numerous. The fact that such unusual communicating junctions were not found in any other region of the lens leads us to speculate that structural changes in fiber cell communicating junctions may herald the formation of fusion zones and that the initial site of cell-to-cell fusion between fiber cells may be within communicating junctional plaques.

Comparison of the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures

We evaluated the effects of argon fluoride (ArF) and krypton fluoride (KrF) excimer lasers on ocular structures. We produced corneal incisions, optical iridotomy, capsulotomy, and retinotomy with these lasers. Incisions produced with ArF showed sharply defined borders with minimal coagulative effects to the adjacent structures. Cuts created with KrF showed coagulative necrosis of the wound edges ranging from two to five um in width. From our study it appears that ArF has photoablative action and KrF has a predominantly photoablative action with minimal photocoagulative effect on the tissue.

A correlative freeze-etch and electrophysiological study of communicating junctions in crystalline lenses

We have conducted a correlative electrophysiological and morphological study of cell to cell coupling in frog and rat lenses. Electrical impedance measurements from frog and rat lenses were curve fit to a model of lens structure to obtain a value for internal resistivity (Ri). The mean and standard deviation of Ri was 550 +/- 190 ohm-cm (n = 7) in rat lenses and 3400 +/- 340 ohm-cm (n = 10) in frog lenses. These results indicate that the extent of cell to cell coupling is far more extensive in rat lenses than in frog lenses and therefore suggest that rat lens fiber cells are conjoined by greater numbers of communicating junctions than frog lens fiber cells. Freeze-etch replicas were made of fiber cells from rat and frog lenses of comparable size and from a comparable area (intermediate cortex) as that used in the electrophysiological study. A total of 987 and 1,393 square microns of replicated membrane were examined in rat and frog lenses, respectively. 1,573 communicating junctions were counted in rat lens replicas cumulatively measuring 313 square microns or 31.7% of the total membrane area. 604 communicating junctions were counted in frog lens replicas cumulatively measuring 163 square microns or 11.7% of the total membrane area. These results demonstrate that the amount of communicating junction predicted to be necessary to account for the more extensive electrotonic coupling between fiber cells in rat lenses than in frog lenses is qualitatively confirmed by morphological analysis.

The use of procion dyes for light microscopy of the frog lens

Protocols for light microscopy of frog lenses that result in good visibility of cell structure from the lens surface to its nucleus are presented. The lenses are fixed in 10% neutral formalin in 0.06 M phosphate buffer and are embedded in Epon 812. Following staining of the thick sections with selected Procion dyes, essentially every cell in the section plane of the lens can be visualized by simple light microscopy without fluorescence. The methods and dyes allow measurement of cell dimensions at all depths in the lens and allow investigation of cell packing geometry. The techniques should be generally useful for studying normal lens structure and the alteration of structure induced by cataractogenesis.

The electrical coupling of epithelium and fibers in the frog lens

Electrical coupling has been measured between central epithelial cells and fiber cells in the frog lens following the removal of the lens capsule with collagenase. Current passed from a microelectrode inserted in a lens fiber cell was found to induce a potential difference in epithelial cells which was indistinguishable from that measured in nearby fiber cells. The measurements were made under circumstances where the current and voltage microelectrodes could be shown to be in different cells and an intraepithelial location of the voltage-measuring microelectrode could be verified. The electrical coupling appears to be direct from superficial fiber cells to epithelial cells, rather than indirect through equatorial epithelial cells. The epithelial cells and surface fiber cells each had resting potentials of -61.8 +/- 2.1 mV in this collagenase-treated preparation. Scanning electron microscopy (SEM) of mechanically decapsulated frog lenses showed specialized junction-like plaques on the expanded anterior ends of fiber cells which made contact with epithelial cells. Such specialized plaques were not found on the expanded posterior ends of these fibers where they contracted the posterior capsule. The studies provide direct evidence for cell-to-cell communication between frog lens epithelial cells and fibers.

A simple fluorescence technique for light microscopy of the crystalline lens

Lenses fixed in formaldehyde or glutaraldehyde can be embedded in plastic, and sections as large as 3-4 mm across can be cut with glass knives on an ultramicrotome. When these sections are stained with 25% sodium fluorescein and allowed to bleach in a fluorescence microscope, high contrast images of essentially every cell in the section, including cells very near the lens center, can be seen. The method is effective with lenses from a number of species, and should be useful for a wide variety of morphological studies of normal and cataractous lenses.