Aprotinin reduces ischemia-reperfusion injury in the retina of guinea pigs

PURPOSE: The aim of this study was investigate the role of aprotinin on retinal lipid peroxidation and histopathological changes during ischemia/reperfusion (I/R) of guinea pigs. METHODS: Three groups of seven pigmented guinea pigs each were formed: a control (group 1), ischemia/saline (group 2) and ischemia/aprotinin (group 3). One eye of each animal was selected for histopathological evaluation and the other for biochemical assay. Bilateral pressure-induced retinal ischemia was instigated for 90 min and was followed by 24 hours of reperfusion. Animals in the ischemia/aprotinin and ischemia/saline groups received either 20,000 KIU/kg of aprotinin or saline, repeated four times at 6-hour intervals, with the first dose administered 5 min prior to the ischemic insult. The animals were killed at 24 hours of reperfusion. Retinal malondialdehyde (MDA) levels and the thickness of the inner plexiform layers were measured. RESULTS: The level of MDA in group 1 was significantly (p<0.001) lower than the other groups. The mean MDA level in group 2 was significantly (p<0.01) higher than in group 3. The inner plexiform layer in group 1 was significantly (p<0.001) thinner than in the other groups. The mean thickness of the inner plexiform layer in group 2 was significantly (p<0.01) higher than in group 3. CONCLUSIONS: These data indicate that intraperitoneally administrated aprotinin has a protective effect against I/R injury in the retina of guinea pig as evidenced by reduced retinal MDA level and retinal thickness.     

Effects of melatonin,vitamin E and octreotide on lipid peroxidation during ischemia-reperfusion in the guinea pig retina

PURPOSE: The purpose of this study is to provide evidence that free radical damage is a component of retinal ischemia-reperfusion (I/R) injury, and to determine whether melatonin, vitamin E and octreotide can protect the retina from this injury. METHODS: The right eyes of 50 male guinea pigs weighing 500-600 g were used. The animals were randomly assigned to group 1 (control), group 2 (I/R), group 3 (melatonin + I/R), group 4 (vitamin E + I/R) and group 5 (octreotide + I/R). Groups 3, 4 and 5 received four subcutaneous injections with a 6-h interval for a total daily dose of 10 mg/kg melatonin, 150 mg/kg vitamin E and 22 microg/kg octreotide. The first dose of each substance was administered 5 minutes before retinal ischemia, which was induced for 1.5 hours, followed by reperfusion for 24 hours. All three substances were repeated for 6, 12 and 18 hours during reperfusion. The animals were killed at 24 hours of reperfusion. Retinas were isolated and processed for the quantification of malondialdehyde (MDA). RESULTS: The compounds had the following relationships: melatonin more than vitamin E more than octreotide in preventing retinal damage by ischemia-reperfusion. All three gave significantprotection against the formation of MDA (10.4+/-2.3, 12.4+/-2.4, 13.9+/-1.5 nmol/100 mg tissue wet weight, respectively) compared to the control (3.7+/-1.3 nmol/100 mg tissue wet weight) and I/R groups (22.7+/-6.2 nmol/100 mg tissue wet weight). CONCLUSIONS: This study demonstrates the inhibitory effect of melatonin, vitamin E and octreotide on MDA levels during retinal ischemia-reperfusion injury.     

Effects of intraperitoneal vitamin E, melatonin and aprotinin on leptin expression in the guinea pig eye during experimental uveitis

PURPOSE: To observe ultrastructural changes and leptin expression in the guinea pig eye during experimental uveitis (EU) and the effects of vitamin E, melatonin and aprotinin on leptin expression. METHODS: Thirty male guinea pigs were randomly classified into five groups. Group 1 was the control group. Groups 2, 3, 4 and 5 received intravitreal injections of bovine serum albumin (BSA) to induce EU. At the same time on the third day, groups 3 (EU + vitamin E), 4 (EU + melatonin) and 5 (EU + aprotinin) received intraperitoneal vitamin E (150 mg/kg), melatonin (10 mg/kg) and aprotinin (20,000 IU/kg), respectively. On the sixth day, histopathological and clinical scoring of inflammation were performed, and leptin expression was investigated in the retina, choroid, sclera, episclera and cornea, and compared. RESULTS: There was a remarkable increase in leptin expression in the retina, choroid, sclera and episclera in the EU group. Leptin expression in the treatment groups was similar to that in the control group. At light and electron microscopic levels, ganglion cells were oedematous and inner plexiform layer thickness had increased in the EU group retinas. Oedema was decreased in the treatment groups. Comparison of the EU and treatment groups revealed significant differences histopathologically and clinically. CONCLUSION: Experimental uveitis causes an increase in leptin expression in the retina, choroid, sclera and episclera of guinea pigs. Vitamin E, melatonin and aprotinin inhibit this increase. Leptin seems to be closely related to ocular inflammation.     

Protection by dimethylthiourea against retinal light damage in rats.

The protective effect of dimethylthiourea (DMTU) against retinal light damage was determined in albino rats reared in darkness or in weak cyclic light. Rats maintained under these conditions were treated with DMTU at different concentrations and dosing schedules and then exposed for various times to intense visible light, either intermittently (1 hr light and 2 hr dark) or continuously. The extent of retinal light damage was determined 2 weeks after light exposure by comparing rhodopsin levels in experimental rats with those in unexposed control animals. To determine the effect of DMTU on rod outer segment (ROS) membrane fatty acids, ROS were isolated immediately after intermittent light exposure, and fatty acid compositions were measured. The time course for DMTU uptake and its distribution in serum, retina, and the retinal pigment epithelium (RPE)/choroid complex was determined in other rats not exposed to intense light. After intraperitoneal injection of the drug (500 mg/kg body weight), DMTU appeared rapidly in the serum, retina, and the RPE and choroid. In the ocular tissues, it was distributed 70-80% in the retina and 20-30% in the RPE and choroid. This antioxidant appears to have a long half-life because it was present in these same tissues 72 hr after a second intraperitoneal injection. For rats reared in the weak cyclic light environment, DMTU (two injections) provided complete protection against rhodopsin loss after intense light exposures of up to 16 hr. Only 15% rhodopsin loss was found in cyclic-light DMTU-treated rats after 24 hr of intermittent or continuous light. For rats reared in darkness, DMTU treatment resulted in a rhodopsin loss of less than 20% after 8-16 hr of continuous light and approximately 40% after similar exposure to intermittent light. Irrespective of the type of light exposure, rhodopsin loss in the dark-reared DMTU-treated rats was nearly identical to that found in uninjected cyclic light-reared animals. In rats from both light-rearing environments, DMTU treatment prevented the light-induced loss of docosahexaenoic acid from ROS membranes. As measured by rhodopsin levels 2 weeks later, DMTU was most effective when given as two doses administered 24 hr before and just before intense light exposure. As a single dose given during continuous light exposure, DMTU protected cyclic light-reared rats for at least 4 hr after the start of exposure but was ineffective in dark-reared animals if injected 1 hr after the start of light. It was also ineffective in both types of rats when given after light exposure.(ABSTRACT TRUNCATED AT 400 WORDS)     

维生素E对大剂量蓝光诱导损伤视网膜色素上皮细胞的影响

目的:研究维生素E(Vit E)对大剂量蓝光诱导人视网膜色素上皮(hRPE)细胞损伤的影响,为减少蓝光损伤hRPE细胞的预后方案提供思路。方法:用3000±150Lx蓝光建立hRPE细胞损伤模型;利用流式细胞术检测照射时间分别为0、3、6、9、12、24h的6组hRPE细胞凋亡率及活性氧相对量;利用流式细胞术检测照射0h组、照射6h组、照射6h前或后加不同浓度Vit E组(Vit E的浓度分别为10、50、100μmol/L)的hRPE细胞凋亡情况和活性氧相对量,并采用Hoechst 33258试剂染色在荧光显微镜下观察hRPE细胞的荧光强度。结果:与照射0h组相比,照射3、6、9、12、24h组的hRPE细胞活性氧相对量明显增加(均P<0.01),照射6、9、12、24h组的hRPE细胞凋亡率也明显增加(均P<0.01),但照射3h组的hRPE细胞凋亡率无明显增加,差异无统计学意义(P=0.46)。与照射6h组相比,除照射6h前加入10μmol/L的hRPE细胞凋亡率(P=0.66)外,其他加Vit E的实验组hRPE细胞活性氧相对量和凋亡率明显减少、细胞中Hoechst 33258释放蓝色荧光逐渐减弱,且呈浓度依赖(均P<0.01)。与照射0h组相比,加Vit E的6组hRPE细胞活性氧相对量和凋亡率有差异(均P<0.01)。同一浓度的Vit E,除10μmol/L Vit E的hRPE细胞凋亡率在照射前或后加无差异(P=0.08)外,照射后加Vit E组比照射前加Vit E组的hRPE细胞活性氧相对量、凋亡率明显减少(均P<0.01)。结论:hRPE细胞经蓝光照射后出现胞内活性氧相对量增多的现象早于细胞凋亡,清除胞内活性氧是减少大剂量蓝光诱导hRPE细胞损伤的思路。Vit E可保护由大剂量蓝光诱导的RPE细胞损伤,这种效应随Vit E浓度增加而增强,且照射后加入比照射前加入的效果更好。但需要一定剂量的Vit E才能显效,而且无法完全修复损伤。     

The protective effects of melatonin,vitamin E and octreotide on retinal edema during ischemia-reperfusion in the guinea pig retina

PURPOSE: The purpose of this study is to provide evidence that free radical damage is a component of retinal ischemia-reperfusion (I/R) injury, and to determine whether melatonin, vitamin E and octreotide can protect retina from this injury. METHODS: The right eyes of 50 male guinea pigs weighing 500-600 g were used. The animals were randomly assigned to group 1 (control), group 2 (I/R), group 3 (melatonin + I/R), group 4 (vitamin E + I/R) and group 5 (octreotide + I/R). Groups 3, 4 and 5 received four subcutaneous injections at six-hour intervals for total dosage of 10 mg/kg melatonin, 150 mg/kg vitamin E and 22 microg/kg octreotide respectively. The first dose of each substance was administered 5 minutes before retinal ischemia. Retinal ischemia was induced for 1.5 hours, then followed by reperfusion for 24 hours. Infections of all three substances were repeated at 6, 12 and 18 hours during reperfusion. The animals were killed at 24 hours of reperfusion. Sagittal sections of 4 microm were cut and stained with hematoxylin and eosin for light microscopic evaluation. The average thickness (edema) of the inner plexiform layer for each eye was measured in sagittal sections near the optic nerve and expressed in microns. RESULTS: The efficacy of each compound had the following relationships: melatonin>vitamin E>octreotide in preventing retinal damage by ischemia-reperfusion. The mean thickness of the inner plexiform layer was 13.3 +/- 0.8 microm, 25.9 +/- 2. 0 microm, 20.0 +/- 0. 7 microm, 21.6 +/- 0.7 microm, 23.9 +/- 0.8 microm respectively in the control, I/R, I/R plus melatonin, I/R plus vitamin E and I/R plus octreotide groups. The thickness of the inner plexiform layer in group 1 (control) was significantly less than the other groups (p<0.001). The inner plexiform layer was thicker in the I/R group than with I/R plus melatonin, I/R plus vitamin E and I/R plus octreotide (all p < 0.01). The inner plexiform layer was thicker in the I/R plus octreotide group than the I/R plus vitamin E and I.R plus melatonin groups both (p < 0.05). Compared to the I/R plus melatonin group, the inner plexiform layer was significantly thicker in the I/R plus vitamin E group (p < 0. 05). CONCLUSIONS: This study demonstrates a protective effect of melatonin, vitamin E and octreotide on the retina during retinal ischemia-reperfusion injury.     

Inhibition of DNA and RNA synthesis in lymphocyte cultures by rod outer segments and its counteraction by vitamin E and other antioxidants

Bovine rod outer segments (ROS) specifically stimulate DNA synthesis in lymphocyte cultures from guinea pigs preimmunized with ROS. At doses above 10 microgram/ml protein, however, preparations of ROS inhibit DNA and RNA synthesis by the sensitized lymphocytes or by normal lymphocytes reacting to mitogens. The inhibtion of RNA synthesis becomes apparent after 24 hr of incubation, whereas little effect was detected after 6 hr. Of the lymphocytes tested, those from mouse and guinea pig spleen were the most susceptible to the effects of ROS, whereas were completely refractory to tested doses of ROS. Bovine retina homogenates were moderately inhibitory, whereas the corresponding cytosol fractions had no detectable effect. Intact ROS were less inhibitory than the disrupted ones, but only minimal amounts of inhibitory activity leaked from disrupted ROS during incubation. Two ROS components, retinoids and docosahexaenoic acid, were also inhibitory to the lymphocytes. The effects of ROS, retinoids, or docosahexaenoic acid were counteracted by antioxidants, with alpha-tocopherol (vitamin E) providing the best protection against ROS. These data thus show lymphocyte cultures to be useful for studying the damaging potential of ROS components and the essential role of antioxidants in protecting the retinal tissues.     

Photoreceptor physiology in the rat is governed by the light environment

Albino rats were born and raised in one of three cyclic (12L: 12D) lighting conditions: (1) 5 lux for 9 weeks, (2) 800 lux for 9 weeks, or (3) 800 lux for 9 weeks, followed by 5 lux for 3 weeks (800:5). After the treatment, the following were determined: (i) retinal function as measured by the electroretinogram (ERG); (ii) retinal morphology, including rod outer segment (ROS) length and outer nuclear layer area; (iii) rhodopsin levels in whole retina and ROS preparations; (iv) fatty acid profile of ROS membranes and (v) retinal antioxidant levels. After 9 weeks, rats raised in 800 lux sustained an irreversible loss of photoreceptors which could not be reversed by then placing them in 5 lux. However, these rats displayed significant alterations in all other parameters measured after the 3 weeks in dim cyclic light. ERGs showed a 60% increase of b-wave maximum amplitude in 800:5 rats at 12 weeks over the value at the time of their change to a dim environment, while a-wave amplitude in 800:5 rats increased more than 2.5 times. This increase can be explained by a combination of increased ROS length and increased ROS membrane concentration of rhodopsin during the three weeks in 5 lux. Polyunsaturated fatty acids predominated in the ROS of 5 lux rats and 800:5 rats, but not in 800 lux animals. Measurements of retinal glutathione enzyme activity and vitamin E and C levels were relatively low in 800:5 rats. Some rats from the 800:5 group were exposed to 2000 lux for 24 hr. Retinas of these rats sustained 50% loss of photoreceptors from this exposure. Comparisons are made to previous studies concerning the effect of cyclic light environments on the retinas of albino rats.     

Polyunsaturated fatty acids and vitamin E in rat rod outer segments during light damage

Previous evidence suggests that lipid peroxidation may initiate photoreceptor damage induced by constant light exposure. In order to investigate the role of the antioxidant vitamin E in light damage, Long-Evans (pigmented) rats were atropinized and exposed to constant fluorescent light (Vita-Lite) of 10-20 foot candles for intervals up to 5 days. Following light exposure, retinal rod outer segments (ROS) were prepared and their lipids extracted. Retinas processed in parallel for morphological examination showed progressive ROS deterioration and selective loss of photoreceptor cells at 3 and 5 days of constant light. Similar to previous observations in undilated albino rats, constant illumination resulted in the specific loss of docosahexaenoic acid (22:6 omega 3) in the ROS. A novel finding in this study was an increase in the content of vitamin E relative to lipid phosphorus, stearic acid, and docosahexaenoic acid in the ROS of constant light-exposed animals.     

Effect of light history on retinal antioxidants and light damage susceptibility in the rat

Albino rats were born and raised to 12 weeks of age in 12L:12D light regimes of 5, 300 or 800 lx. Upon killing, the activities of the following glutathione enzymes were measured in the neuroretina: (1) glutathione peroxidase; (2) glutathione-S-transferase; and (3) glutathione reductase. Also measured were vitamin E, ascorbic acid, and the levels of oxidized and reduced glutathione. Animals raised in 800-lx cyclic light have a significant increase in the retinal activities of the three glutathione enzymes over activities measured in animals raised in the two dimmer regimes. The retinal level of vitamin E, measured per nmol of lipid phosphorus, is directly and significantly correlated with rearing illuminance (P less than 0.05). The same is true of retinal ascorbic acid, which shows a 30% increase in the 800-lx-reared rats over the level of those raised in the intermediate light regime (300 lx). Some of the animals from each group were exposed to 2000 lx for 24 hr to determine if correlations existed between the levels of retinal antioxidants listed above and susceptibility to light damage. Animals raised in 5-lx cyclic light lost almost all of their photoreceptors as a result of the exposure. Rats raised in 300-lx cyclic light lost a small but significant number (ca. 20%), while those raised in 800 lx sustained no light damage. Electroretinographic evaluation supports these morphometrical findings.     

L-carnitine in experimental retinal ischemia-reperfusion injury

The effect of L-carnitine on retinal ischemia-reperfusion injury was evaluated in guinea pigs. 90 min of pressure-induced retinal ischemia followed by 24 h of reperfusion was established in both eyes of 2 groups of animals receiving either L-carnitine (100 mg/kg repeated in 5 doses) or saline intraperitoneally. After enucleation of all the eyes, including those of a control group, malonyldialdehyde (MDA) levels and the thickness of the retinal tissue were measured in 3 groups. The mean MDA value and the tissue thickness of the L-carnitine-treated group were statistically insignificant versus the control group (p > 0.05 and p > 0.05, respectively). However, these values were significantly different in the group receiving saline versus the control group and that receiving L-carnitine (p < 0.001, p < 0.001 and p < 0.001, p < 0.001 respectively). L-Carnitine might be an alternative drug for ischemia-reperfusion injury of the retina.     

Calcium antagonists in<Emphasis Type="Italic"> N</Emphasis>-methyl <Emphasis Type="SmallCaps">d</Emphasis>-aspartate-induced retinal injury

PURPOSE: To detect the neuroprotective role of nimodipine and dantrolene in N-methyl- d-aspartate (NMDA)-induced retinal injury. METHODS: In this study we used two calcium antagonists which have two different modes of action, nimodipine and dantrolene, to prevent NMDA-induced retinal ischemia in guinea pigs. In 40 animals we injected nimodipine (n=10), dantrolene (n=10), a combination of both (n=10) or sterile 0.9% NaCl solution as a placebo (n=10) before intravitreal injection of NMDA. We enucleated one eye of each animal after 48 hours and performed histopathologic examination. We also measured malondialdehyde (MDA) levels in retinal homogenates as a marker of ischemic injury. RESULTS: Our results indicate that ganglion cells of the retina were preserved mostly by nimodipine, followed by combined nimodipine-dantrolene, and dantrolene respectively. The ganglion cell count was statistically significantly higher in cases where we used calcium antagonists than in the control group (p<0.05). We also found that MDA was significantly reduced by calcium antagonists compared to the control group (p<0.05). CONCLUSION: Our data show that nimodipine and dantrolene both have potential neuroprotective effects; nimodipine preserved retinal ganglion cells to a greater extent than dantrolene from NMDA-induced retinal injury.     

Failure of vitamin E to protect the retina against damage resulting from bright cyclic light exposure

Cumulative light-mediated damage to the retina over a long time period may be involved in the development of age-related retinopathies. Light is thought to produce retinal damage by initiating autoxidative reactions among the molecular components of the retina. Experiments were therefore conducted (1) to confirm that long-term differences in cyclic light intensity affect the rate of age-related photoreceptor cell loss from the retina; and (2) to determine whether the antioxidant, vitamin E, is an effective inhibitor of damage to the retina by bright cyclic light. Albino rats were fed a basal diet either supplemented with or deficient in vitamin E. Each dietary group was divided into two light-treatment groups which were exposed to 12 hr cyclic light of either 15 lux or 750 lux. After 10 and 17 weeks of treatment, retinal photoreceptor cell densities were determined for animals in each group. Vitamin E deficiency resulted in moderate decreases in photoreceptor cell densities in the dim-light groups after both 10 and 17 weeks. Rats exposed to the bright-light condition suffered a pronounced loss of photoreceptor cells by 10 weeks, and an even greater cell loss by 17 weeks. Vitamin E deficiency did not enhance the effect of bright cyclic light in reducing photoreceptor cell densities. Thus, it appears unlikely that retinal damage by cyclic light occurs via an autoxidative mechanism.     

Protection of photoreceptor cells in adult rats from light-induced degeneration by adaptation to bright cyclic light

Light history has been shown to affect the susceptibility of the albino rat retina to the damaging effects of constant light exposure. Retinas of animals raised in relatively bright cyclic light are protected against light-induced degeneration compared with dim-reared animals. These effects were observed in animals raised from birth in bright cyclic light and are part of an adaptive response that protects photoreceptors from stress-induced degeneration. To determine if retinas of adult animals are capable of such adaptive changes or flexibility by switching between different light environments which do not pathologically damage photoreceptor cells, albino rats were maintained in less than 250 lux cyclic light for more than 3 weeks. At 12-13 weeks of age, they were placed into 800 lux cyclic light for 1 week, after which they were exposed to constant illumination of 1500-lux for 1, 3 or 7 days. Retinal function was evaluated by electroretinography and photoreceptor cell death was quantified by measuring outer nuclear layer thickness. After 1 week in bright cyclic light, the retinas were completely protected against 1 day constant light exposure that significantly damaged retinas of animals without 800 lux cyclic light adaptation. Significant protection was also observed in 3 day constant light exposed animals; limited protection occurred after 7 days exposure. These results indicate that the retinas of adult rats adapted to bright cyclic light within certain ranges that did not significantly damage photoreceptor cells are protected from constant light challenge. This phenomenon is a post-developmental response that demonstrates a remarkable plasticity of the retina. The mechanism(s) underlying the ability of this adaptation/flexibility in protecting photoreceptors could involve endogenous molecules that encompass many aspects of retinal cell and molecular biology and physiology. Identification of these molecules may provide insight into the development of therapeutic approaches to treat retinal degeneration.     

枸杞子提取物对光诱导视网膜损伤的保护作用

目的　探索枸杞子提取物对人视网膜色素上皮（ARPE-19）细胞及C57BL/6J小鼠视网膜光诱导损伤的保护作用。方法　ARPE-19细胞分为正常细胞对照组,光诱导细胞损伤组,细胞低、中、高剂量组（0.1 g·L^-1、0.5 g·L^-1、1.0 g·L^-1枸杞子提取物+光诱导细胞损伤）,测定各组细胞活力以及细胞内活性氧（ROS）含量的变化。40只C57BL/6J小鼠随机分为正常动物对照组,光诱导动物损伤组,动物低、中、高剂量组（280 mg·kg^-1、370 mg·kg^-1、460 mg·kg^-1枸杞子提取物+光诱导动物损伤组）,每组8只。各剂量枸杞子提取物干预组小鼠在6周龄开始给予枸杞子提取物灌胃,8周后再给予10 000 lux光照射24 h;光照结束后ERG评估各组小鼠视网膜功能,OCT检测视网膜外核层（ONL）厚度,FFA检测视网膜血管渗漏情况,HE染色后对视网膜ONL细胞进行计数,同时检测血清中丙二醛（MDA）含量和超氧化物歧化酶（SOD）、谷胱甘肽过氧化物酶（GSH-Px）活性。结果　光诱导细胞损伤组ARPE-19细胞活力下降为正常细胞对照组的61.88%,细胞内ROS含量为正常细胞对照组的1.52倍;细胞低、中、高剂量组ARPE-19细胞活力较光诱导细胞损伤组均明显上升,细胞内ROS含量均明显下降,并均呈剂量依赖性（均为P＜0.05）。与动物对照组相比,光诱导动物损伤组小鼠ERG暗适应a波、b波振幅和明适应b波振幅均明显下降,动物低、中、高剂量组各波的振幅均得到不同程度改善。光诱导动物损伤组小鼠视网膜出现萎缩灶、血管渗漏和血管末端成珠样结构,视网膜ONL厚度变薄,为（52.18±4.23) μm,ONL每列细胞数明显减少,为（17.63±1.30）个;动物低、中、高剂量组小鼠视网膜病理改变及视网膜ONL厚度与ONL每列细胞数均得到不同程度改善,尤其动物高剂量组改善最为明显,ONL厚度为（59.72±2.76）μm, ONL每列细胞数为（20.00±1.51）个,与光诱导动物损伤组相比差异均有统计学意义（P=0.007、0.004）。相对于光诱导动物损伤组,动物低、中、高剂量组小鼠血清SOD、GSH-Px活性均明显提高,MDA含量均明显下降,且均呈剂量依赖性（均为P＜0.05）。结论　枸杞子提取物可以一定程度上保护视网膜免受光损伤。     

Neuroprotection of photoreceptors by minocycline in light-induced retinal degeneration

PURPOSE: Microglial cells have been found to play pivotal roles in various neuronal degenerative diseases such as Parkinson's and Alzheimer's diseases. Minocycline, a microglial inhibitor, has recently been shown to be neuroprotective in various models of cerebral ischemia and degenerative diseases of the brain. This study was conducted to evaluate the neuroprotective effect of minocycline and the role of microglia in light-induced retinal degeneration. METHODS: BALB/cJ mice were exposed to intense green light for 3 hours and observed during 1, 3, or 7 days of dark recovery. The animals received intraperitoneal injections of minocycline or vehicle 1 day before exposure to light for 2, 4, or 8 days, depending on the periods of survival. Morphologic, morphometric, immunohistochemical, and electrophysiological studies were performed to evaluate the efficacy of minocycline in the amelioration of light-induced retinal degeneration and the possible involvement of microglial cells. RESULTS: Minocycline treatment provided marked amelioration in the loss of photoreceptors in light-induced retinal degeneration, as evidenced by morphologic, morphometric, and electrophysiologic criteria. Morphologically, the minocycline-treated group showed markedly better preservation of the outer retina after exposure to light. Morphometrically, at 7 days after exposure to light, in the minocycline-treated animals, 89.1% of the normal-appearing photoreceptor nuclei remained, but in the retinas of the vehicle-control group only 38.0% of these nuclei remained. This difference was statistically significant (P < 0.001). At 7 days after exposure to light electroretinography (ERG) showed that minocycline significantly preserved the amplitudes of dark-adapted a- and b-wave and light-adapted b-wave, which were all significantly reduced after exposure to light. Concomitant with this protective effect, at 3 days after exposure to light, the CD11b(+) microglial cells in the outer nuclear layer (ONL) and subretinal space in the minocycline-treated group were significantly decreased (by 63.5%) when compared with those in the light-exposed, vehicle-treated control group (P < 0.01). CONCLUSIONS: Minocycline is neuroprotective against light-induced loss of photoreceptors, possibly through the inhibition of retinal microglial activation.     

Melatonin increases photoreceptor susceptibility to light-induced damage.

Melatonin is an indolamine hormone synthesized in the retina and pineal gland. It is thought to act as a paracrine neurohormone in the mammalian retina. Pinealectomy has been shown to protect photoreceptors from light-induced damage, and melatonin treatment has been reported to increase the degree of photoreceptor damage in albino rats. To determine how melatonin influences photoreceptor survival, the effect of melatonin administration on light-induced retinal damage was studied. Melatonin was administered to albino rats by intraperitoneal injections at various times before or after light exposure. The rats were exposed to high-intensity illumination (1600 lux) for 24 hr to induce photodamage, then returned to cyclic lighting for 12 days. After this, they were killed, and their eyes were removed and examined histologically. Measurements of the outer nuclear layer (ONL) thickness were taken at 12 different loci around the circumference of the retinal sections. The animals that received daily melatonin injections (100 micrograms) in the late afternoon (3 hr before lights off) for 1-3 days before photodamage showed an approximate 30% greater reduction compared with sham control animals in ONL thickness in the superior quadrant, the area most susceptible to light damage. Melatonin injections given after the photodamage did not affect ONL thickness. Although retinal susceptibility to light damage varied with time of day, the degree to which melatonin increased the degree of damage appeared unaffected by the time of day. These results suggest that melatonin may be involved in some aspects of photoreceptor sensitivity to light damage.     

Susceptibility to retinal light damage in transgenic rats with rhodopsin mutations

PURPOSE: To determine relative light-induced retinal damage susceptibility in transgenic rats expressing mutations in the N- or C-terminal region of rhodopsin. METHODS: Heterozygous transgenic rats, including P23H sublines 2 and 3 and S334ter sublines 4 and 9, were reared in dim cyclic light or in darkness before visible light exposure starting at various times of the day or night. Before exposure to light, some rats were given the synthetic antioxidant dimethylthiourea (DMTU). At various times after intense light treatment, rats were killed for determinations of rhodopsin and retinal DNA recovery, DNA fragmentation patterns, and Northern blot analysis of retinal heme oxygenase (HO)-1 and interphotoreceptor retinol binding protein (IRBP). Rod outer segments (ROSs) were isolated for Western blot analysis of rhodopsin using N- and C- terminal-specific monoclonal antibodies. RESULTS: All rats incurred greater photoreceptor cell damage from exposure to light starting at 1 AM than from exposure at 5 PM. Among cyclic-light-reared rats, P23H line 3 animals were more susceptible to light-induced damage than P23H line 2 animals. S334ter rats exhibited retinal light damage profiles similar to those in normal rats. Dark-rearing potentiated retinal damage by light. However, dark-rearing alone prolonged photoreceptor cell life in P23H rats, but had no such effect in S334ter animals. DMTU pretreatment was effective in preventing or reducing light-induced retinal damage in all transgenic rats. S334ter rat ROSs contained the truncated form of rhodopsin. Intense light exposure resulted in DNA ladders typical of apoptotic cell death and the simultaneous induction of retinal HO-1 mRNA and reduced expression of IRBP. CONCLUSIONS: Light-induced retinal damage in transgenic rats depends on the time of day of exposure to light, prior light-or dark-rearing environment, and the relative level of transgene expression. Retinal light damage leads to apoptotic visual cell loss and appears to result from oxidative stress. These results suggest that reduced environmental lighting and/or antioxidant treatment may delay retinal degenerations arising from rhodopsin mutations.     

视网膜光损伤机制的研究进展

视网膜是一种高度专业化的组织,具有独特的结构及适应性,在所有不同类型的视网膜细胞中保持动态平衡对于维持视力至关重要。视网膜可能会暴露在各种环境损伤中,如光诱导的损伤,在进化过程中,视网膜细胞对各种损伤产生了适应性反应,这些反应共同恢复了细胞的动态平衡,并增加了组织对进一步损伤的抵抗力。然而过度光照则会导致视网膜组织内光感受器细胞、视网膜神经节细胞(RGC)、视网膜神经胶质细胞及视网膜色素上皮细胞(RPE)发生一系列病理改变,包括线粒体内活性氧(ROS)和Ca²⁺浓度增加、细胞凋亡、内质网应激、细胞自噬和炎症等,从而导致视网膜发生不可逆损伤。本文将对视网膜光损伤的发病机制和相关研究进展进行详细阐述,为未来防治视网膜光损伤提供研究方向。