Ординатура / Офтальмология / Английские материалы / Ocular Neuroprotection_Levin, Polo _2003
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duced retinal light damage [52] and c-fos knockouts [29] and the absence of RPE-65, which is required for rhodopsin regeneration [53], prevents light damage [54]. These studies and others [47,55] have provided useful insights into the mechanisms of inherited retinal degenerations and retinal light damage.
Using transgenic rats with a P23H rhodopsin mutation or an S-334 truncation, provided by M. LaVail, we compared their relative susceptibilities to retinal light damage. Figure 6 is an example of results from rats reared in different light environments and exposed to intense green light.
Overall, P23H line 3 rats were more susceptible than line 2 rats, which have a slower rate of spontaneous retinal degeneration (LaVail, personal communication), S-334 ter line 4 and line 9 rats were equally damaged by light when previously reared in dim cyclic light. Why a folding mutation in the amino terminal region of rhodopsin leads to greater light damage susceptibility than the loss of 15 amino acids from the C-terminal region is unknown at present. However, these transgenic rats appear to be good models of some forms of human retinitis pigmentosa because the loss of rod photoreceptors is accelerated by intense light [56].
In recent studies we found that normal rats exhibit both increased light damage susceptibility and resistance to light damage, depending only on the time of day that light exposure begins [42]. A circadian response was also found to exist in transgenic P23H and S-334 ter rats [8]. This indicates that endogenous factors normally expressed in the retina contribute to light damage susceptibility and that systemic or local signals in the retina may regulate their expression.
A variety of growth factors also provide neuroprotection in rats given intraocular injections prior to light exposure [57]. As these neurotrophic factors are normally given in microgram concentrations 2 days before a 1-week intense light treatment, it appears that they elicit changes in the expression of other retinal proteins that provide protection. In a follow-up study, LaVail and associates found that β-FGF induced a dose-dependent expression of the transcription factors c-fos and c-jun in isolated rat Muller cells. [58]. There are two important points to be made from studies such as these. The first is that these factors work at low concentrations in a doseand time-dependent manner in rats. The same may not hold for other rodents, such as mice, which reemphasizes the need for
Cyclic Reared
Normal S-334, line 9 line 4 P23H, line 2 line 3 Dark Reared
Normal S-334, line 4 line 9 P23H, line 2 line 3
Figure 6 Relative light damage susceptibility in different rat models. Results are based on end point determinations of rhodopsin and DNA in comparison to their respective unexposed controls. Normal Sprague-Dawley rats are least susceptible to light damage.
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careful species selection. The second point is that trauma to the injected eye can induce a stress response, as shown by partial protection in the eyes of vehicle injected animals. LaVail et al. [57] controlled for this partial response, further supporting their important conclusions regarding neurotrophic factors.
2. Exogenous Treatments or Factors
A variety of natural or synthetic compounds have been shown to provide protection against retinal light damage. In fact, a colleague once asked, “is there anything that does not protect the retina against light damage?”(personal communication, B. Winkler). Quite simply, the answer is yes. The same compounds that exhibit protection provide no effect when given at the wrong time, at the wrong concentration, or in the wrong way. There are also a number of variables associated with exogenous agents and neuroprotection in the light damage model. These include systemic versus local effects, concentration, uptake and half-life or clearance rates, as well as time and intensity relationships during light exposure. In this section we describe some of these variables in the rat model.
First and foremost the question of efficacy is a function of the extent of light-induced damage. In our model the goal is to induce 50% photoreceptor cell loss in untreated or vehicle-injected rats. In doing so, it is possible to reliably determine whether a drug protects against or enhances retinal light damage by measuring an increase or decrease in visual cell survival. Too much damage can overcome a protective effect and too little can mask the effect. In this type of experiment, the variable most often applied is duration of exposure at a fixed light intensity. With the use of a 50% cell response, it is also possible to compare the relative efficacy of a variety of drugs or closely related compounds. Using such an approach we were able to demonstrate that the synthetic antioxidant dimethylthiourea (DMTU) was more effective in reducing light damage than L- ascorbic acid, a natural antioxidant present in the retina [59]. It is important to note that the D-steroisomer of ascorbate, which is an antioxidant but not an enzymatic cofactor in mammals, was as effective as L-ascorbate when given at an equal concentration [59].
A second variable is tissue uptake and the half-life of administered compounds. For cyclic light–reared rats treated with DMTU, we found complete protection following light exposures lasting for up to 48 h. By measuring tissue levels, we found that DMTU has a half-life of about 24 h [60], whereas ascorbic acid has a much shorter half-life (4–8 h). DMTU levels in the retina were also about fivefold higher than L-ascorbate 10 min after IP injection. As serum levels of drugs can also be high, it is important to use perfused animals for accurate retinal tissue level measurements. We estimate that the rat retina contains about 10 L of blood. Accordingly, to demonstrate uptake in a tissue such as the retina, if the animal is not perfused, the concentration of drug should be higher than in blood.
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A surprising number of studies report protection against retinal light damage without measurements of the nature described above. Thus, it is never really clear whether the administered compound is itself active in preventing the damage or whether it exerts a systemic, perhaps stress, effect leading to protection. Ideally, an agent that exhibits a primary effect not only will be present in the retina for a period of time but also will be found at lower levels in the eyes of light-treated animals than in unexposed controls. The level of ascorbic acid, for example, can be shown to decrease in the rat retina during light exposure and to be effective only when given before the start of light treatment [61,62].
To achieve effective levels of drugs in the eye, the route of administration and the type of compound are also important. We have had good success with water-soluble antioxidants such as DMTU and ascorbic acid given I.P., I.V., or I.O. The kinetics of uptake for ascorbate in retina or RPE are similar for I.P. and I.O. injections although, as expected, the concentrations in the two tissues and the time courses of their losses were different [62]. The same is not true, however, for lipid soluble materials such as β-carotene or other carotenoids. The reasons for this are not entirely clear. Using I.P. or oral gavage of these materials in rats, we have been unsuccessful in demonstrating efficient retinal uptake. It appears that detergents will be required to solubilize these lipophylic materials for possible tissue uptake and light damage studies.
Finally, a comment about dose response curves. Whether one chooses to measure tissue uptake or not, or to determine serum levels and clearance rates, a dose response curve for any drug or compound can be informative and useful in
Figure 7 Dose-response curves for antioxidants used in light damage. Rhodopsin measured 2 weeks after intense light exposure. (A) 8 h ( ) or 3 h ( ) of intermittent light. (B) 24 h ( ) or 12 h ( ) continuous light. ( , ) cyclic light and dark reared rats. (A) ( , ) urea; (B) ( ) dehydroascorbic acid; (A) ( , ■) unexposed controls S.D. (n 8–12).
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studies of neuroprotection. These responses can be different for different animal models. As shown in Figure 7, the level of antioxidant required for maximal effectiveness is not the same for rats reared in dim cyclic light or in darkness.
First the level of tissue damage in the two types of rats is different. Second, the concentration of injected DMTU or ascorbate required to reach a plateau effect is greater in dark reared rats [60,61]. This is important because working with lower concentrations will not achieve the same level of protection, compromising the drugs’ effect. In practice, we use a concentration well above the minimum to achieve protection because this gives a more uniform response among test subjects. This translates into more reliable results with fewer animals required for light damage studies.
IV. CONCLUSIONS
In the preceding we have attempted to provide an experimental outline for studies related to acute retinal light damage and neuroprotection in vivo. By addressing some problems and pitfalls we hope that future investigators will avoid some of the common mistakes that we and others have made. While a number of mechanistic interpretations might be derived from such studies, the effects of light on genetically modified animals, and the prevention of vision loss, has implications well beyond the use of the models described here. For the present these experimental outcomes will need to be extrapolated to the human condition. However, with a better understanding of the variables associated with acute light damage, we may find simple dietary or other therapeutic approaches to neuroprotection for those afflicted with genetic or age related vision loss.
ACKNOWLEDGMENTS
Supported by NIH grant EY-01959; Ohio Lions Research Foundation; and M. Petticrew, Springfield, OH.
REFERENCES
1.Lanum J. The damaging effects of light on the retina: Emperical findings, theoretical and practical implications. Survey Ophthal 1978; 22:221–249.
2.Kremers JJM, van Norren D. Two classes of photochemical damage of the retina. Lasers and Light in Ophthalmology 1988; 2:41–52.
3.Organisciak DT, Winkler BS. Retinal light damage: Practical and theoretical considerations. In: Osborne N, Chader G, eds. Progress in Retinal and Ocular Research. Oxford, England: Pergamon Press; 1994:1–29.
104 |
Organisciak et al. |
4.Rapp LM. Retinal phototoxicity. In: Chang LW, Dyer RS, eds. Handbook of Neurotoxicology. New York: Marcel Dekker; 1995: 32:963–1003
5.Reme´ CE, Weller M, Szczesny P, Munz K, Hafezi F, Reinboth JJ, Clausen M. Light-induced apoptosis in the rat retina in vivo: morphologic features, threshold and time course. In: Anderson RE, LaVail MM, Hollyfield JG, eds. Degenerative Diseases of the Retina. New York: Plenum Press; 1995:19–25.
6.Reme´ CE, Hafezi F, Marti K, Munz, Reinboth JJ. Light damage to retina and pigment epithelium. In: Marmor MF, Wolfensberger TJ, eds. The Retinal Pigment Epithelium: Function and Disease. New York: Oxford University Press; 1998:563–586.
7.Winkler BS, Boulton ME, Gottsch JD, Sternberg P. Oxidative damage and agerelated macular degeneration. Mol Vis 1999; 5:1–19.
8.Organisciak DT, Sarna T. Genetic, age and light induced degenerations of the retina and retinal pigment epithelium. In: Coohill TP, Valenzena DP, eds. Photobiology for the 21st Century. Overland Park, Kansas: Valdenmar Publishing Co.; 2001:81– 100
9.Lawwill T. Effects of prolonged exposure of rabbit retina to low intensity light. Invest Ophthalmol Vis Sci 1973; 12:45–51.
10.Collier RJ, Zigman S. Comparison of retinal photochemical lesions after exposure to near-UV or short-wavelength visible radiation. In: LaVail MM, Anderson RE, Hollyfield JG, eds. Inherited and Environmentally Induced Retinal Degenerations. New York: Alan R. Liss; 1989:569–575.
11.Fite KV, Bengston L, Donaghey B. Experimental light damage increases lipofuscin in the retinal pigment epithelium of Japanese quail. Exp Eye Res 1993; 57:449– 460.
12.Dureau P, Jeanny JC, Clerc B, Dufier J-L, Courtois Y. Long term light-induced retinal degeneration in the miniature pig. Mol Vis 1996; 2:7–14.
13.Sperling HG. Prolonged intense spectral light effects on Rhesus retina. In: Williams TP, Baker BN, eds. The Effects of Constant Light on Visual Processes. New York: Plenum Press; 1980:195–214.
14.Li L, Dowling JE. Zebrafish visual sensitivity is regulated by a circadian clock. Vis Neurosci 1998; 15:851–857.
15.Allen DM, Hallows TE. Solar pruning of retinal rods in albino rainbow trout. Vis Neurosci 1997; 14:589–600
16.Moritz OL, Tom BM, Knox BE, Papermaster DS. Fluorescent photoreceptors of transgenic xenopres laevis imaged in vivo by two microscopy techniques. Invest Ophthalmol Vis Sci 1999; 40:3276–3280.
17.Williams TP, Thistle AB, Eds. Photostasis and Related Phenomena. New York: Plenum Press; 1998.
18.Meyer-Rochow VB. Light induced damage to photoreceptors of spiny lobsters and other crustaceans. Crustaceana 1994; 67:95–109.
19.Kashiwagi T, Meyer-Rochow VB, Nishimura K, Eguchi E. Fatty acid composition and ultra structure of photoreceptive membrane in the crayfish under conditions of thermal and photic stress. J Comp Physiol B 1997; 167:1–8.
20.Allen DM, Pipes C, Deramus K, Hallows TE. A comparison of light-induced rod degeneration in two teleost models. In Hollyfield et al., eds. Retinal Degenerative Diseases and Experimental Therapy. New York: Plenum Publishers; 1999:337–350.
Light-Induced Retinal Degeneration |
105 |
21.Yoon J, Ben-Ami HG, Hong YS, Park S, Strong KK, Bowman J, Geng C, Baek KB, Minke B, Pak WL. Novel mechanism of massive photoreceptor degeneration caused by mutations in the trp gene of Drosophilia. J Neurosci 2000; 20:649–659.
22.LaVail MM. Survival of some photoreceptor cells in albino rats following longterm exposure to continuous light. Invest Ophthalmol Vis Sci 1976; 15:64–70.
23.LaVail MM, Gorrin GM, Repaci MA. Strain differences in sensitivity to lightinduced photoreceptor degeneration in albino mice. Curr Eye Res 1987; 6:825– 834.
24.LaVail MM, Gorrin GM, Repaci MA, Thomas LA, Ginsberg HM. Genetic regulation of light damage to photoreceptors. Invest Ophthalmol Vis Sci 1987; 28:1043– 1048.
25.Noell WK, Walker VS, Kang BS, Berman S. Retinal damage by light in rats. Invest. Ophthalmol 1966; 5:450–473.
26.Rapp LM,Williams TP. A parametric study of retinal light damage in albino and pigmented rats. In: Williams TP, Baker BN, eds. The Effects of Constant Light on Visual Processes. New York: Plenum Press; 1980:133–159.
27.Naash ML, Peachey NS, Li Z-Y, Gryczan CC, Goto Y, Blanks J, Milam AH, Ripps H. Light-induced acceleration of photoreceptor cell degeneration in transgenic mice expressing mutant rhodopsin. Invest Ophthalmol Vis Sci 1996; 37:775–782.
28.Green ES, Meng MD, LaVail MM, Flannery JG. Characterization of rhodopsin missorting and constitutive activation in a transgenic rat model of retinitis pigmentosa. Invest Ophthalmol Vis Sci 2000; 41:1546–1553.
29.Hafezi F, Steinbach JP, Marti A, Munz K, Wang ZQ, Wagner EF, Aguzzi A, Reme´ CE. The absence of c-fos prevents light-induced apoptotic cell death of photoreceptors in retinal degeneration in vivo. Nat Med 1997; 3:346–349.
30.Organisciak, DT, Li M, Darrow RM, Farber DB. Photoreceptor cell damage by light in young Royal College of Surgeons rats. Curr Eye Res 1999; 2:188– 196.
31.Penn JS, Anderson RE. Effect of light history on rod outer segment membrane composition in the rat. Exp. Eye Res 1987; 44:767–778.
32.Penn JS, Naash ML, Anderson RE. Effect of light history on retinal antioxidants and light damage susceptibility in the rat. Exp Eye Res 1987; 44:779–788.
33.Organisciak DT, Xie A, Wang H-M, Jiang Y-L, Darrow RM, Donoso LA. Adaptive changes in visual cell transduction protein levels: Effect of light. Exp Eye Res 1991; 53:773–779.
34.Organisciak DT, Darrow RM, Noell WK, Blanks JC. Hyperthermia accelerates retinal light damage in rats. Invest Ophthalmol Vis Sci 1995; 36:997–1008.
35.Grimm C, Reme´ CE, Rol PO, Williams TP. Blue light’s effects on rhodopsin: photoreversal of bleaching in living rat eyes. Invest Ophthalmol Vis Sci 2000; 41:3984– 3990.
36.De Lint PJ, van Norren D, Toebosch AMW. Effect of body temperature on threshold for retinal light damage. Invest Ophthalmol Vis Sci 1992; 33:2382–2387.
37.Organisciak DT, Jiang Y-L, Wang H-M, Pickford M, Blanks JC. Retinal light damage in rats exposed to intermittent light. Comparison with continuous exposure. Invest Ophthalmol Vis Sci 1989; 30:795–805.
38.Noell WK. There are different kinds of retinal light damage in rats. In: Williams
106 |
Organisciak et al. |
TP, Baker BN, eds. The Effects of Constant Light on Visual Processes. New York: Plenum Press; 1980:3–28.
39.Organisciak DT, Darrow RM, Barsalou L, Darrow RA, Kutty RK, Kutty G, Wiggert BN. Light history and age-related changes in retinal light damage. Invest Ophthalmol Vis Sci 1998; 39:1107–1116.
40.Noell WK, Albrecht R. Irreversible effects of visible light on the retina: Role of vitamin A. Science 1971; 172:76–80.
41.Organisciak DT, Darrow RM, Jiang YL, Blanks JC. Retinal light damage in rats with altered levels of rod outer segment docosahexaenoate. Invest Ophthalmol Vis Sci 1996; 37:2243–2257.
42.Organisciak DT, Darrow RM, Barsalou L, Kutty RK, Wiggert B. Circadian dependent retinal light damage in rats. Invest Ophthalmol Vis Sci 2000; 41:3694–3701.
43.Keller C, Grimm C, Wenzel A, Hafezi F, Reme´ CE. Halothane anesthesia inhibits rhodopsin regeneration and prevents photoreceptor degeneration in the rodent retina. Invest Ophthalmol Vis Sci 2001; 2001; 42:476–480.
44.Sugawara T, Sieving PA, Bush RA. Quantitative relationship of the scotopic and photopic ERG to photoreceptor cell loss in light damaged rats. Exp Eye Res 2000; 70:693–705.
45.Darrow RA, Darrow RM, Organisciak DT. Biochemical characterization of cell specific enzymes in light-exposed rat retinas: Oxidative loss of all-trans retinol dehydrogenase activity. Curr Eye Res 1997; 16:144–151.
46.Organisciak DT, Darrow RA, Barsalou L, Darrow RM, Lininger LA. Light induced damage in the retina: differential effects of dimethylthiourea on photoreceptor survival, apoptosis and DNA oxidation. Photochem Photobiol 1999; 70:261–268.
47.Joseph RM, Li T. Overexpression of Bcl-2 or Bcl-xL transgenes and photoreceptor degeneration. Invest Ophthalmol Vis Sci 1996; 37:2434–2446.
48.Kueng-Hitz, N, Grimm C, Lansel N, Hafezi F, He L, Fox DA, Reme´ CE, Niemeyer G, Wenzel A. The retina of cfos -/- mice: electrophysiologic, morphologic and biochemical aspects. Invest Ophthalmol Vis Sci 2000; 41:909–916.
49.LaVail MM, Battelle BA. Influence of eye pigmentation and light deprivation on inherited retinal dystrophy in the rat. Exp Eye Res 1975; 21:167–192.
50.Noell WK. Hereditary retinal degeneration and damage by light. In: Estratto dagli Atti Simposio di Oftalmologia Pediatrica. Marccari Parma; 1974:322–329.
51.Mittag TW, Bayer AU, LaVail MM. Light-induced retinal damage in mice carrying a mutated SOD 1 gene. Exp Eye Res 1999; 69:677–683.
52.Chen J, Simon MI, Matthes MT, Yasumura D, LaVail MM. Increased susceptibility to light damage in an arrestin knockout model of Oguchi disease (Stationary night blindness). Invest Ophthalmol Vis Sci 1999; 40:2978-2982.
53.Redmond MT, Yu S, Lee E, Bok D, Hamasaki D, Chen N, Goletz P, Ma J-X, Crouch R, Pfeifer K. Rpe65 is necessary for production of 11-cis-vitamin A in the retinal visual cycle. Nat Genet 1998; 20: 344–351.
54.Grimm C, Wenzel A, Hafezi F, Yu S, Redmond M. Protection of Rpe65-deficient mice identifies rhodopsin as mediator of light-induced retinal degeneration. Nat Genet 2000; 25:63–66.
55.Hobson AH, Donovan M, Humphries MM, Tuohy G, McNally N, Carmody R, Cotter T, Farrar GJ, Kenna PF, Humphries P. Apoptotic photoreceptor cell death
Light-Induced Retinal Degeneration |
107 |
in the rhodopsin knockout mouse in the presence and absence of c-fos. Exp Eye Res 2000; 71:247–254.
56.Heckenlively JR, Rodriguez JA, Daiger SP. Autosomal dominant sectoral retinitis pigmentosa: Two families with transversion mutations in codon 23 of rhodopsin. Arch Ophthalmol 1991; 109:84–91.
57.LaVail MM, Unoki K, Yasumura D, Matthes MT, Yancopoulos GD, Steinberg RH. Multiple growth factors, cytokines, and neurotrophins rescue photoreceptors from the damaging effects of constant light. Proc Natl Acad Sci USA 1992; 89:11249– 11253.
58.Cao W, Li F, Steinberg RH, LaVail MM. Induction of c-fos and c-jun mRNA expression by basic fibroblast growth factor in cultured rat Muller cells. Invest Ophthalmol Vis Sci 1998; 39: 656–573.
59.Organisciak DT, Darrow RM, Bicknell IR, Jiang Y-L, Pickford M, Blanks JC. Protection against retinal light damage by natural and synthetic antioxidants. In: Anderson RE, Hollyfield MM, LaVail MM, eds. Retinal Degenerations. Boca Raton, FL: CRC Press; 1991:189–201.
60.Organisciak DT, Darrow RM, Jiang YL, Marak GE, Blanks JC. Protection by dimethylthiourea against retinal light damage in rats. Invest Ophthalmol Vis Sci 1992 33:1599–1609.
61.Organisciak DT, Wang HM, Li ZY, Tso MOM. The protective effect of ascorbate in retinal light damage of rats. Invest Ophthalmol Vis Sci 1985; 26:1580–1588.
62.Organisciak DT, Bicknell IR, Darrow RM. The effects of L- and D- ascorbic acid administration on retinal tissue levels and light damage in rats. Curr Eye Res 1992; 11:231–241.
63.Organisciak DT, Wang H-M, Xie A, Reeves DS, Donoso LA. Intense-light mediated alterations in rat rod outer segment lipids and proteins. In: LaVail MM, Anderson RE, Hollyfield JG, eds. Inherited and Environmentally Induced Retinal Degenerations. New York: Alan Liss, Inc., 1989:493–512.
7
Retinal Detachment
Ward M. Peterson
Inspire Pharmaceuticals
Durham, North Carolina, U.S.A.
I.INTRODUCTION
Retinal detachment is an acute pathological endpoint of many ocular conditions and often results in permanent impairment of central vision if the macula is detached. Models of experimental retinal detachment (RD) have been developed to understand the disease process and to provide insight into various aspects of basic retinal biology. For reviews of significant findings made in the context of experimental RD, see Refs. [1–3]. Although naturally occurring retinal detachments have been observed in cats, dogs, and monkeys, these occur too infrequently to be useful as reliable model systems [4–8]. To mimic various aspects of the clinical condition, a number of experimental models of RD have been developed using surgical and, to a lesser extent, pharmacological means. On the cellular level, sustained retinal alterations and photoreceptor degeneration are common outcomes of prolonged detachments (3). The significance of retinopathic changes in causing protracted or permanent visual dysfunction in patients suffering from retinal detachment is well appreciated [3,9]. However, investigations of experimental models of RD in the context of either reducing the severity or enhancing the recovery of retinal function are considerably limited.
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