Norman J. Kleiman

Risk for radiation-induced cataract for staff in interventional cardiology: Is there reason for concern?†‡

Objectives: To examine the prevalence of radiation‐associated lens opacities among interventional cardiologists and nurses and correlate with occupational radiation exposure. Background: Interventional cardiology personnel are exposed to relatively high levels of X‐rays and based on recent findings of radiation‐associated lens opacities in other cohorts, they may be at risk for cataract without use of ocular radiation protection. Methods: Eyes of interventional cardiologists, nurses, and age‐ and sex‐matched unexposed controls were screened by dilated slit lamp examination and posterior lens changes graded using a modified Merriam‐Focht technique. Individual cumulative lens X‐ray exposure was calculated from responses to a questionnaire and personal interview. Results: The prevalence of radiation‐associated posterior lens opacities was 52% (29/56, 95% CI: 35–73) for interventional cardiologists, 45% (5/11, 95% CI: 15–100) for nurses, and 9% (2/22, 95% CI: 1–33) for controls. Relative risks of lens opacity was 5.7 (95% CI: 1.5–22) for interventional cardiologists and 5.0 (95% CI: 1.2–21) for nurses. Estimated cumulative ocular doses ranged from 0.01 to 43 Gy with mean and median values of 3.4 and 1.0 Gy, respectively. A strong dose–response relationship was found between occupational exposure and the prevalence of radiation‐associated posterior lens changes. Conclusions: These findings demonstrate a dose dependent increased risk of posterior lens opacities for interventional cardiologists and nurses when radiation protection tools are not used. While study of a larger cohort is needed to confirm these findings, the results suggest ocular radio‐protection should be utilized.

Radiation Cataract Risk in Interventional Cardiology Personnel

Abstract The lens of the eye is one of the most radiosensitive tissues in the body, and exposure of the lens to ionizing radiation can cause cataract. Cumulative X-ray doses to the lenses of interventional cardiologists and associated staff can be high. The International Commission on Radiological Protection recently noted considerable uncertainty concerning radiation risk to the lens. This study evaluated risk of radiation cataract after occupational exposure in interventional cardiology personnel. Comprehensive dilated slit-lamp examinations were performed in interventional cardiologists, associated workers and controls. Radiation exposures were estimated using experimental data from catheterization laboratories and answers to detailed questionnaires. A total of 116 exposed and 93 similarly aged nonexposed individuals were examined. The relative risk of posterior subcapsular opacities in interventional cardiologists compared to unexposed controls was 3.2 (38% compared to 12%; P < 0.005). A total of 21% of nurses and technicians had radiation-associated posterior lens changes typically associated with ionizing radiation exposure. Cumulative median values of lens doses were estimated at 6.0 Sv for cardiologists and 1.5 Sv for associated medical personnel. A significantly elevated incidence of radiation-associated lens changes in interventional cardiology workers indicates there is an urgent need to educate these professionals in radiation protection to reduce the likelihood of cataract.

Scanning Slit Confocal Microscopic Observation of Cell Morphology and Movement within the Normal Human Anterior Cornea

PURPOSE Noninvasive in vivo observations of the anterior human cornea were performed to study cell structure and dynamics. Cellular elements were identified by their location, morphology, and pattern of movement. The hypothesis that cells in the epithelial layer of the normal cornea migrate centripetally was tested. METHODS Using a scanning slit confocal microscope with a new 0.75-numeric aperture contact objective, individual cells of normal human corneas were observed over time, quantifying the velocity and direction of cellular movement within the basal epithelial layer. RESULTS Basal epithelial cells, wing cells, the basal epithelial nerve plexus, and the subepithelial nerve plexus were identified readily. Centripetal motion was observed for three corneal cell types: basal epithelial cells, basal epithelial nerves, and unidentified cellular elements (possibly Langerhans cells). The unidentified cellular elements moved along the length of the basal epithelial nerves. The basal epithelial nerve plexus maintained a roughly stable topology as it slid centripetally. New nerve material appeared at the site of entry of the nerve into the epithelium. No growth cones were present at the distal termini of the growing epithelial nerves. CONCLUSION In the midperiphery of the normal human cornea, basal epithelial cells and nerves slide centripetally, probably in concert. Unidentified cellular elements used the basal epithelial nerve plexus as a pathway for intraepithelial movement. Observations in this study suggest that neurite growth occurred by the addition of new membrane material along the length of the axon rather than at a distal growth cone.

Radiation-associated Lens Opacities in Catheterization Personnel: Results of a Survey and Direct Assessments

PURPOSE To estimate ocular radiation doses and prevalence of lens opacities in a group of interventional catheterization professionals and offer practical recommendations based on these findings to avoid future lens damage. MATERIALS AND METHODS Subjects included 58 physicians and 69 nurses and technicians attending an interventional cardiology congress and appropriate unexposed age-matched controls. Lens dose estimates were derived from combining experimental measurements in catheterization laboratories with questionnaire responses regarding workload, types of procedures, and use of eye protection. Lens opacities were observed by dilated slit lamp examination using indirect illumination and retroillumination. The frequency and severity of posterior lens changes were compared between the exposed and unexposed groups. The severity of posterior lens changes was correlated with cumulative eye dose. RESULTS Posterior subcapsular lens changes characteristic of ionizing radiation exposure were found in 50% of interventional cardiologists and 41% of nurses and technicians compared with findings of similar lens changes in<10% of controls. Estimated cumulative eye doses ranged from 0.1-18.9 Sv. Most lens injuries result after several years of work without eye protection. CONCLUSIONS A high prevalence of lens changes likely induced by radiation exposure in the study population suggests an urgent need for improved radiation safety and training, use of eye protection during catheterization procedures, and improved occupational dosimetry.

A brief photochemically induced oxidative insult causes irreversible lens damage and cataract. II. Mechanism of action.

Using photochemically induced oxidative stress and rat lenses in organ culture with 4% O2 and 4 microM riboflavin, it has been found that the observed changes in lens parameters are, in most cases, irreversible. This has made possible the elucidation of the sequence of biological changes leading to cataract. The earliest detectable changes in lens cell biology are observed in the epithelial cell redox set point and at the DNA level in terms of DNA integrity and 3H-thymidine incorporation followed by decreased membrane transport and changes in gene expression. Significant modification in classical cataract parameters such as hydration, steady state non-protein thiol, glyceraldehyde-phosphate-dehydrogenase activity and transparency occur at later times. The data suggest a definitive pattern of lens breakdown resulting in opacity starting at the epithelial cell level and leading to subsequent fibre cell involvement.

Hydrogen peroxide-induced DNA damage in bovine lens epithelial cells

The present investigation was undertaken to determine the types and extent of DNA damage resulting from incubation of primary cultures of bovine lens epithelial cells with hydrogen peroxide. Significant numbers of DNA single-strand breaks were detected by alkaline elution after exposure to as little as 25 microM H2O2 for 5 min at 37 degrees C. The extent of single-strand breakage was concentration dependent and linear from 25 to 200 microM H2O2. The observed single-strand breaks appear primarily due to the action of the hydroxyl radical via a Fenton reaction as both an iron chelator, 1,10-phenanthroline and OH. scavengers, including DMSO, KI and glycerol, significantly inhibited the DNA-damaging effect of H2O2. Diethyldithiocarbamate, an inhibitor of superoxide dismutase, further potentiated the DNA-damaging effects of H2O2, presumably by increasing the steady-state concentration of Fe2+. DNA-protein cross-linking was not observed. In addition, significant levels of 5,6-saturated thymine residues or pyrimidine dimers were not detected after modification of the alkaline elution methodology to allow the use of either E. coli endonuclease III or bacteriophage T4 endonuclease V, respectively. No double-strand breaks were detected after incubation of epithelial cell cultures with H2O2 concentrations of up to 400 microM for 10 min and subsequent neutral filter elution. Since, in vivo, the lens epithelium contains populations of both quiescent and dividing cells, the degree of susceptibility to oxidative damage was also studied in actively growing and plateau-phase cultures. Reduced levels of single-strand breakage were observed when plateau-phase cultures were compared to actively growing cells. In contrast, essentially no differences in repair rates were noted at equitoxic doses of H2O2. The above results suggest that lens epithelial cells may be particularly sensitive to oxidative damage and thus are a good model system in which to study the effects of oxidative stress.

Ultraviolet light induced DNA damage and repair in bovine lens epithelial cells

DNA damage caused by UV-B and UV-A irradiation and the rate of repair of such damage was quantitated in bovine lens epithelial cell cultures using a modified alkaline elution methodology. Two enzymes, bacteriophage T4 endonuclease V, which cleaves at the site of pyrimidine dimers, and E. coli endonuclease III, which cleaves at the site of thymine glycols, were utilized. Pyrimidine dimers were not detected after UV-A irradiation of lens cultures with up to 400 J/m2. In contrast, after exposure to as little as 2 J/m2 of UV-B irradiation, large numbers of pyrimidine dimers were observed. At higher fluences, thymine glycols were also found. Significant levels of DNA-DNA crosslinking were suggested by reduced rates of elution of DNA from cells treated with both UV-B irradiation and H2O2 in comparison to treatment with H2O2 alone. Protein-DNA crosslinks, in contrast, were not observed. The rate of repair of UV-B induced DNA damage was quantitated by harvesting cells at various times after the UV-B exposure. Single-strand breaks were never observed immediately after UV-B exposure but appeared later during the repair phase. In contrast to the repair of H2O2 induced DNA damage, which is largely completed within 30 min of exposure, more than 50% of the UV-B light induced DNA damage remained unrepaired five hours after exposure. This difference between the rate of repair of H2O2 and UV-B induced DNA damage could provide valuable insights into the nature of DNA damaging agents in the lens environment and may reflect underlying differences in the potential for epithelial cell DNA mutation in response to various DNA damaging insults.

Loss of ephrin-A5 function disrupts lens fiber cell packing and leads to cataract

Cell–cell interactions organize lens fiber cells into highly ordered structures to maintain transparency. However, signals regulating such interactions have not been well characterized. We report here that ephrin-A5, a ligand of the Eph receptor tyrosine kinases, plays a key role in lens fiber cell shape and cell–cell interactions. Lens fiber cells in mice lacking ephrin-A5 function appear rounded and irregular in cross-section, in contrast to their normal hexagonal appearance in WT lenses. Cataracts eventually develop in 87% of ephrin-A5 KO mice. We further demonstrate that ephrin-A5 interacts with the EphA2 receptor to regulate the adherens junction complex by enhancing recruitment of β-catenin to N-cadherin. These results indicate that the Eph receptors and their ligands are critical regulators of lens development and maintenance.

Radiation and cataract

When this paper was about to go to press, the International Commission on Radiological Protection released a statement recommending a change in the threshold dose for the eye lens and dose limits for eye for occupationally exposed persons. It is clear that the earlier published threshold for radiation cataract is no longer valid. Epidemiological studies among Chernobyl clean-up workers, A bomb survivors, astronauts, residents of contaminated buildings, radiological technicians and recent surveys of staff in interventional rooms indicate that there is an increased incidence of lens opacities at doses below 1 Gy. Nevertheless, eye lens dosimetry is at a primitive stage and needs to be developed further. Despite uncertainties concerning dose threshold and dosimetry, it is possible to significantly reduce the risk of radiation cataract through the use of appropriate eye protection. By increasing awareness among those at risk and better adoption and increased usage of protective measures, radiation cataract can become preventable despite lowering of dose limits.

The phosphorylation sites of the B2 chain of bovine α-crystallin

Abstract The B 2 chain of bovine lens α-crystallin is phosphorylated in a cAMP-dependent reaction. By analysis of 32 P-labelled chymotryptic peptides isolated from α-crystallin obtained from lenses labelled in organ culture, two phosphorylated B 2 chain fragments were found. Sequence analysis of the fragments gave the following results: Arg-Ala-Pro-Ser-Trp-Ile-Asp-Thr-Gly-Leu and Ser-Leu-Ser-Pro-Phe corresponding to residues 56 to 65 and 43 to 47, respectively. It is established by this work that B 1 is a phosphorylated post-translational product of B 2 . Both the A 2 and B 2 chains of α-crystallin are phosphorylated at a similar site with the sequence Arg-(X)-Pro-Ser. This is an unusual site for cAMP-phosphorylation since the phosphorylated serine is preceded by a proline residue. It may also be of significance that the other B 2 chain phosphorylation site even more radically differs from previously reported cAMP-dependent phosphorylation sites.