Basil V. Worgul

Cataracts among Chernobyl Clean-up Workers: Implications Regarding Permissible Eye Exposures

Abstract Worgul, B. V., Kundiyev, Y. I., Sergiyenko, N. M., Chumak, V. V., Vitte, P. M., Medvedovsky, C., Bakhanova, E. V., Junk, A. K., Kyrychenko, O. Y., Musijachenko, N. V., Shylo, S. A., Vitte, O. P., Xu, S., Xue, X. and Shore, R. E. Cataracts among Chernobyl Clean-up Workers: Implications Regarding Permissible Eye Exposures. Radiat. Res. 167, 233–243 (2007). The eyes of a prospective cohort of 8,607 Chernobyl clean-up workers (liquidators) were assessed for cataract at 12 and 14 years after exposure. The prevalence of strictly age-related cataracts was low, as expected (only 3.9% had nuclear cataracts at either examination), since 90% of the cohort was younger than 55 years of age at first examination. However, posterior subcapsular or cortical cataracts characteristic of radiation exposure were present in 25% of the subjects. The data for Stage 1 cataracts, and specifically for posterior subcapsular cataracts, revealed a significant dose response. When various cataract end points were analyzed for dose thresholds, the confidence intervals all excluded values greater than 700 mGy. Linear-quadratic dose–response models yielded mostly linear associations, with weak evidence of upward curvature. The findings do not support the ICRP 60 risk guideline assumption of a 5-Gy threshold for “detectable opacities” from protracted exposures but rather point to a dose–effect threshold of under 1 Gy. Thus, given that cataract is the dose-limiting ocular pathology in current eye risk guidelines, revision of the allowable exposure of the human visual system to ionizing radiation should be considered.

Atm heterozygous mice are more sensitive to radiation-induced cataracts than are their wild-type counterparts

It is important to know whether the human population includes genetically predisposed radiosensitive subsets. In vitro studies have shown that cells from individuals homozygous for ataxia telangiectasia (A-T) are much more radiosensitive than cells from unaffected individuals. Although cells heterozygous for the ATM gene (ATM+/−) may be slightly more radiosensitive in vitro, it remained to be determined whether the greater susceptibility of ATM+/− cells translates into an increased sensitivity for late effects in vivo, though there is a suggestion that radiotherapy patients that are heterozygous for the ATM gene may be more at risk of developing late normal tissue damage. We chose cataractogenesis in the lens as a means to assay for the effects of ATM deficiency in a late-responding tissue. One eye of wild-type, Atm heterozygous and homozygous knockout mice was exposed to 0.5-, 1.0-, 2.0-, or 4.0-Gy x rays. The animals were followed weekly for cataract development by conventional slit-lamp biomicroscopy. Cataract development in the animals of all three groups was strongly dependent on dose. The lenses of homozygous mice were the first to opacify at any given dose. Most important in the present context is that cataracts appeared earlier in the heterozygous versus wild-type animals. The data suggest that ATM heterozygotes in the human population may also be radiosensitive. This may influence the choice of individuals destined to be exposed to higher than normal doses of radiation, such as astronauts, and may also suggest that radiotherapy patients who are ATM heterozygotes could be predisposed to increased late normal tissue damage.

Intravitreal Administration of Erythropoietin and Preservation of Retinal Ganglion Cells in an Experimental Rat Model of Glaucoma

Purpose: The aim of this pilot study was to evaluate the potential neuroprotective effect of an intravitreal injection of erythropoietin (EPO) on retinal ganglion cell (RGC) preservation in an episcleral vessel cautery–induced rat model of glaucoma. Methods: The animals were randomly assigned into an unoperated control group (n = 11) and three experimental groups: episcleral vessel cautery only (EVC: n = 4), episcleral vessel cautery with intravitreal normal saline injection (EVC-NS; n = 5), and episcleral vessel cautery with intravitreal EPO treatment (EVC-EPO; n = 9). The intravitreal injections were limited to 5 μl containing either normal saline alone or 200 ng of EPO in normal saline administered immediately after the cautery procedure. RGCs were labeled retrogradely by FluoroGold neuron tracer 5 to 7 days prior to the collection of eyes at day 21 and counted in whole flat-mounted retinas with fluorescence microscopy. Results: Compared to the RGC counts in retinal specimens from unoperated control rats (12,619 ± 310), the corresponding RGC counts were significantly decreased in both the EVC (9116 ± 273; p < 0.005) and EVC-NS (9489 ± 293; p < 0.005) groups but not significantly decreased in the EVC-EPO (11,212 ± 414; p = 0.051) treated retinas. Conclusions: A single intravitreal 200 ng dose of EPO appears to have a protective effect on RGC viability in an in vivo rat model of glaucoma. Further experimental studies are needed to confirm these preliminary results and to optimize the appropriate dose and frequency of EPO delivery in animal models of glaucoma.

The lens epithelium and radiation cataract: IV. Ultrastructural studies of interphase death in the meridional rows

SummaryThe effect of radiation upon the differentiating meridional row cells of the rat lens epithelium was studied by electron microscopy. X-irradiation of rat lenses was shown to disrupt the nuclear and, in some instances, the cytoplasmic organization of these cells.Indications of damage, 4.5 h post-irradiation, are a disruption in the shape of the nucleus and its membranes. This is typified by a bulging or blebbing of the nucleus. At 12 h the affected nuclei deteriorate with obvious membrane breakdown. The nucleoplasm at this time may appear highly condensed and shrunken. Disruption of the plasma membrane is also evident. Based upon previous findings it is likely that the nuclear changes are independent of the processes involved in normal fiber denucleation.

Accelerated Heavy Particles and the Lens

That accelerated heavy ions are highly cataractogenic is indisputable. The basis of heavy particle effectiveness and the augmentation by fractionation, as recently demonstrated, remains less clear. There is no question, however, that these are tied to the ‘track structure’ and densely ionizing nature of the radiation. The unique energy deposition characteristics relating to charge and track structure are now being explored to begin to dissect the cellular response of the lens epithelium to radiation exposure. The elucidation of the basis of the cataractogenic effect of accelerated heavy ions is important not only to risk assessment, but also in the consideration of theories of radiation action and the mechanism of cortical opacification arising from a myriad of cataractotoxic agents.

The reepithelialization of rabbit cornea following partial and complete epithelial denudation.

Abstract The rate of reepithelialization of rabbit corneas following partial and complete epithelial denudation was studied by fluorescein staining, photography, and electron microscopy. Partially denuded corneas healed smoothly but some completely denuded corneas exhibited delayed or regression of healing which was independent of the methods used to denude corneas. Electron microscopy of reepithelializing corneas suggested that polymorphonuclear leucocytes which are present in denuded corneas may influence the course of reepithelialization.

Quantitative comparisons of continuous and pulsed low dose rate regimens in a model late-effect system

PURPOSE There is increasing interest and usage of pulsed low dose rate (PDR) brachytherapy, in which a single source is shuttled through the catheters of an implant, typically for about 10 min each hour. This study was designed to compare the late effects produced in various PDR regimens with those from the corresponding continuous low dose rate (CLDR) regimens. METHODS AND MATERIALS A model late-responding system was used, namely, cataract induction in the rat lens. This system has the advantage of being highly quantifiable. The rats eyes were exposed to a total dose of 15 Gy either continuously over 24 h, or with three different PDR regimens, all with the same total dose and overall time. We addressed three questions: (a) are late effects increased when a CLDR regimen is replaced with 10-min pulses repeated every hour? (b) Are late effects increased if hourly 10-min pulses are replaced with 10-min pulses repeated every 4 h? (c) Are late effects increased if 10-min pulses are replaced with 100-s pulses? RESULTS We found that the four regimens under test, continuous, 10-min pulses each hour, 10-min pulses every 4 h, and 100-s pulses every hour, showed no significant differences in cataractogenic potential, as estimated with the Wilcoxon-Gehan test. Power tests indicated that the experimental design was adequate to detect relatively small differences in cataractogenicity between regimens. CONCLUSIONS The equality of late effects from CLDR and PDR in these experiments must imply that sublethal damage repair is quite slow in this model late-responding system, in agreement with trends observed in the clinic for sublethal damage repair of late sequelae. Such trends would suggest that PDR is unlikely to produce significantly worse late effects than the corresponding CLDR regimen, which is in agreement with early clinical data using PDR. Caution, however, is strongly recommended.

Posterior capsule opacification: experimental analyses

The lenses of New Zealand White and Flemish Giant rabbits were removed using five techniques representative of the different clinical approaches to extracapsular cataract extraction currently employed. Posterior capsule opacification developed in all experimental animals within 6 weeks of the operation. None of the techniques reduced the incidence of the capsular opacification. Histological analyses including immunofluorescent and tritiated thymidine labelling were used to determine the nature of the cellular constitutents of the secondary membrane. The evidence indicates that the opacity is due not only to lens cells remaining after the operation but also consists of cells of nonlenticular origin. The data strongly implicate the anterior uvea as the source of those cells. Furthermore, the findings suggest that posterior capsule opacification is the product of a migration and a proliferation of both cell populations.

Mrad9 and atm haploinsufficiency enhance spontaneous and X-ray-induced cataractogenesis in mice.

Abstract Kleiman, N. J., David, J., Elliston, C. D., Hopkins, K. M., Smilenov, L. B., Brenner, D. J., Worgul, B. V., Hall, E. J. and Lieberman, H. B. Mrad9 and Atm Haploinsufficiency Enhance Spontaneous and X-Ray-Induced Cataractogenesis in Mice. Radiat. Res. 168, 567–573 (2007). Rad9 and Atm regulate multiple cellular responses to DNA damage, including cell cycle checkpoints, DNA repair and apoptosis. However, the impact of dual heterozygosity for Atm and Rad9 is unknown. Using 50 cGy of X rays as an environmental insult and cataractogenesis as an end point, this study examined the effect of heterozygosity for one or both genes in mice. Posterior subcapsular cataracts, characteristic of radiation exposure, developed earlier in X-irradiated double heterozygotes than in single heterozygotes, which were more prone to cataractogenesis than wild-type controls. Cataract onset time and progression in single or double heterozygotes were accelerated even in unirradiated eyes. These findings indicate that the cataractogenic effect of combined heterozygosity is greater than for each gene alone and are the first to demonstrate the impact of multiple haploinsufficiency on radiation effects in an intact mammal. These observations may help explain observed interindividual differential radiosensitivity in human populations and have important implications for those undergoing radiotherapy or exposed to elevated levels of cosmic radiation, such as the astronaut corps. These findings demonstrate that Mrad9 and Atm are important determinants of lens opacification and, given the roles of Atm and Rad9 in maintaining genomic stability, are consistent with a genotoxic basis for radiation cataractogenesis.

Dosimetry for a Study of Low-Dose Radiation Cataracts among Chernobyl Clean-up Workers

Abstract Chumak, V. V., Worgul, B. V., Kundiyev, Y. I., Sergiyenko, N. M., Vitte, P. M., Medvedovsky, C., Bakhanova, E. V., Junk, A. K., Kyrychenko, O. Y., Musijachenko, N. V., Sholom, S. V., Shylo, S. A., Vitte, O. P., Xu, S., Xue, X. and Shore, R. E. Dosimetry for a Study of Low-Dose Radiation Cataracts among Chernobyl Clean-up Workers. Radiat. Res. 167, 606– 614 (2007). A cohort of 8,607 Ukrainian Chernobyl clean-up workers during 1986–1987 was formed to study cataract formation after ionizing radiation exposure. Study eligibility required the availability of sufficient exposure information to permit the reconstruction of doses to the lens of the eye. Eligible groups included civilian workers, such as those who built the “sarcophagus” over the reactor, Chernobyl Nuclear Power Plant Workers, and military reservists who were conscripted for clean-up work. Many of the official doses for workers were estimates, because only a minority wore radiation badges. For 106 military workers, electron paramagnetic resonance (EPR) measurements of extracted teeth were compared with the recorded doses as the basis to adjust the recorded γ-ray doses and provide estimates of uncertainties. Beta-particle doses to the lens were estimated with an algorithm devised to take into account the nature and location of Chernobyl work, time since the accident, and protective measures taken. A Monte Carlo routine generated 500 random estimates for each individual from the uncertainty distributions of the γ-ray dose and of the ratio of β-particle to γ-ray doses. The geometric mean of the 500 combined β-particle and γ-ray dose estimates for each individual was used in the data analyses. The median estimated lens dose for the cohort was 123 mGy, while 4.4% received >500 mGy.