ATF3 Regulates the Expression of AChE During Stress

Acetylcholinesterase (AChE) expresses in non-cholinergic cells, but its role(s) there remain unknown. We have previously attributed a pro-apoptotic role for AChE in stressed retinal photoreceptors, though by unknown mechanism. Here, we examined its promoter only to find that it includes a binding sequence for the activating transcription factor 3 (ATF3); a prototypical mediator of apoptosis. This suggests that expression of AChE could be regulated by ATF3 in the retina. Indeed, ATF3 binds the AChE-promoter to down-regulate its expressions in vitro. Strikingly, retinas of “blinded” mice display hallmarks of apoptosis, almost exclusively in the outer nuclear layer (ONL); coinciding with elevated levels of AChE and absence of ATF3. A mirror image is observed in the inner nuclear layer (INL), namely prominent levels of ATF3 and lack of AChE as well as lack of apoptosis. We conclude that segregated patterns of expressions of ATF3 reflect its ability to repress apoptosis in different layers of the retina—a novel mechanism behind apoptosis.

Infliximab exerts a dose-dependent effect on retinal safety in the albino rabbit

PURPOSE

To assess the retinal toxicity of an intravitreal injection of infliximab, a monoclonal antibody to tumor necrosis factor α, in a rabbit model.

MATERIALS AND METHODS

Two groups of adult albino rabbits (n = 5) received intravitreal injections of infliximab (0.1 ml) in the study eye and balanced salt solution (BSS, 0.1 ml) in the control eye at baseline. Group 1 was administered with 1.5 mg/0.1 ml, and group 2 was injected with 7.5 mg/0.1 ml of infliximab solution. Electroretinography (ERG) was performed at baseline and at 1, 7, 30, and 45 days after the injection. Visual evoked potentials (VEPs) were recorded at 7 and 45 days after the injection. After the last electrophysiological assessment, the rabbits were euthanized and retinal histopathology and immunhistochemistry for glial fibrillary acidic protein (GFAP) were performed.

RESULTS

ERG responses demonstrated no significant deficit in retinal function in eyes injected with infliximab. Mean dark-adapted a-wave and b-wave maximal amplitude and semi-saturation constant values at baseline and throughout the 45 days of follow-up after the injection indicated no remarkable difference in outer retinal function between the control and experimental eyes. VEP responses were similar at each time point (7 and 45 days). No difference was seen in retinal histopathology and immunocytochemistry sections in eyes receiving the 1.5 mg/0.1 ml dose compared to the control eyes. However, increased GFAP labeling in retinal Müller cells was detected in rabbit eyes treated with the 7.5 mg/0.1 ml dose.

CONCLUSIONS

Intravitreal injection of 1.5 mg/0.1 ml infliximab dose has no toxic effect on the integrity (functional or structural) of the retina in rabbits. A higher dose of 7.5 mg/0.1 ml may be slightly toxic as suggested by positive Müller cell GFAP expression. Additional studies of retinal toxicity at higher doses and after multiple injections are needed to establish the retinal safety of intravitreal infliximab therapy in humans.

Light Modulates Ocular Complications in an Albino Rat Model of Type 1 Diabetes Mellitus

PURPOSE

The purpose of the study was to assess potential interactions of light exposure and hyperglycemia upon ocular complications in diabetic rats.

METHODS

Streptozotocin-induced (STZ-induced) diabetic rats (N = 39) and non-diabetic rats (N = 9) were distributed into eight groups according to the irradiance and color of the light phase during the 12/12-hour light/dark regime. Follow-up lasted 90 days and included assessment of cataract development and electroretinogram (ERG) recordings. Stress to the retina was also assessed by glial fibrillary acidic protein immunocytochemistry.

RESULTS

Cataract development was fast in diabetic rats that were exposed to unattenuated white light or to bright colored lights during the light phase. Diabetic rats that were kept under attenuated brown or yellow light during the light phase exhibited slower rate of cataract development. Electroretinogram responses indicated very severe retinal damage in diabetic rats kept under bright colored lights in the blue-yellow range or bright white light during the light phase. Electroretinogram damage was milder in rats kept under bright red light or attenuated yellow or brown light during the light phase. Glial fibrillary acidic protein expression in retinal Müller cells was consistent with ERG assessment of retinal damage.

CONCLUSIONS

Attenuating white light and filtering out short wavelengths have a protective effect on the eyes of diabetic rats as evident by slower rate of cataract formation and a smaller degree of retinal damage.

TRANSLATIONAL RELEVANCE

Our findings suggest that special glasses attenuating light exposure and filtering out short wavelengths (400-530 nm) may be beneficial for diabetic patients.

Tin-carbon clusters and the onset of microscopic level immiscibility: Experimental and computational study

We report the experimental observation and computational analysis of the binary tin-carbon gas phase species. These novel ionic compounds are generated by impact of C60(-) anions on a clean tin target at some kiloelectronvolts kinetic energies. Positive Sn(m)C(n)(+) (m = 1-12, 1 ≤ n ≤ 8) ions were detected mass spectrometrically following ejection from the surface. Impact induced shattering of the C60(-) ion followed by sub-surface penetration of the resulting atomic carbon flux forces efficient mixing between target and projectile atoms even though the two elements (Sn/C) are completely immiscible in the bulk. This approach of C60(-) ion beam induced synthesis can be considered as an effective way for producing novel metal-carbon species of the so-called non-carbide forming elements, thus exploring the possible onset of molecular level miscibility in these systems. Sn2C2(+) was found to be the most abundant carbide cluster ion. Its instantaneous formation kinetics and its measured kinetic energy distribution while exiting the surface demonstrate a single impact formation/emission event (on the sub-ps time scale). Optimal geometries were calculated for both neutral and positively charged species using Born-Oppenheimer molecular dynamics for identifying global minima, followed by density functional theory (DFT) structure optimization and energy calculations at the coupled cluster singles, doubles and perturbative triples [CCSD(T)] level. The calculated structures reflect two distinct binding tendencies. The carbon rich species exhibit polyynic/cummulenic nature (tin end capped carbon chains) while the more stoichiometrically balanced species have larger contributions of metal-metal bonding, sometimes resulting in distinct tin and carbon moieties attached to each other (segregated structures). The Sn2C(n) (n = 3-8) and Sn2C(n)(+) (n = 2-8) are polyynic/cummulenic while all neutral Sn(m)C(n) structures (m = 3-4) could be described as small tin clusters (dimer, trimer, and tetramer, correspondingly) attached to a nearly linear carbon chain. For example, the 1:1 (Sn:C) Sn3C3 and Sn4C4 clusters are composed of all-tin triangle and rhombus, correspondingly, with a short carbon chain (C3, C4) attached on top. The cationic Sn3C(n)(+) (n = 1-5) and Sn4C(n)(+) (n = 1-4) species exhibit various intermediate geometries. Structure calculations at the CCSD(T) level are essential since the segregation effect is not as easily evident based on the most stable structures calculated by DFT alone. Dependences of bond energies (per atom) reflect the evolution of the segregation effect. The mass spectral abundances could be reasonably rationalized in terms of calculated stabilities of the cluster ions with respect to various dissociation channels.

The effects of excitatory amino acids and their transporters on function and structure of the distal retina in albino rabbits

PURPOSE

To study the physiological and pathological roles of excitatory amino acid transporters in the distal retina of albino rabbits.

METHODS

Albino rabbits were injected intravitreally in one eye with different doses of L- or D-isomers of glutamate or aspartate, with mixtures of L-glutamate and antagonists to glutamate receptors or with inhibitors of glutamate transporters. The other eye was injected with saline, and served as a control. The electroretinogram (ERG) was recorded 4 h and 2 weeks after injection. At the end of the ERG follow-up period, retinas were prepared for light microscopy.

RESULTS

The ERG b-wave was reduced and the a-wave augmented by both isomers of EAAs when tested 4 h after injection. Long-term (2-week) follow-up indicated severe damage to the retina by both isomers of EAAs. Antagonists to glutamate-gated ionic channels failed to protect the rabbit distal retina from permanent damage. Competitive inhibitors of GLAST-1 transporter were highly effective in blocking synaptic transmission in the OPL and in inducing permanent ERG deficit. Selective inhibition of the GLT-1 transporter caused short-term augmentation of the ERG and no permanent ERG deficit.

CONCLUSION

GLAST-1, the glutamate transporter of Müller cells, plays a major role in synaptic transmission within the OPL of the rabbit retina. Over-activation of GLAST-1 seems to induce permanent damage to the distal rabbit retina via yet unidentified mechanism.

Physiological and toxicological effects of cefuroxime on the albino rabbit retina

PURPOSE

Intracameral cefuroxime was found to lower the risk of endophthalmitis after cataract surgery. The purpose of this study was to evaluate the retinal toxicity of cefuroxime in a rabbit model.

METHODS

Twenty-two albino rabbits were divided into two cefuroxime groups: low-dose (1mg/0.1 mL, n = 9) and high dose (10 mg/0.1 mL, n = 13). The right eye of each rabbit was injected with 0.1 mL cefuroxime solution (experimental eye) and the left eye with 0.1 mL saline (control eye). Electroretinogram (ERG) responses were recorded at 3 hours, 4 days, and 1, 2, and 4 weeks after injection. After 4 weeks, the rabbits were euthanized, the eyes were enucleated, and the retinas were prepared for histologic evaluation and GFAP immunostaining.

RESULTS

No functional (ERG) or histologic damage was found in rabbits in the low-dose group. In the high-dose group, a significant decrease in the ERG amplitudes of the experimental eyes was seen 3 hours after injection, followed by partial recovery during 4 weeks of follow-up. Retinal histology of experimental eyes revealed marked damage. GFAP immunoreactivity in Müller cells was expressed in rabbits belonging to both groups, although it was more extensive in the high-dose group.

CONCLUSIONS

ERG and histologic findings indicated that a dose of 1 mg cefuroxime, administered intravitreally, was not toxic to the rabbit retina. A dose of 10 mg, injected intravitreally, induced transient physiological effects, and was toxic to the rabbit retina, as was evident by the permanent reduction in the ERG responses and by the structural damage to the retina with signs of glial activation.

RETINAL TOXICITY OF INTRAVITREAL KENALOG IN ALBINO RABBITS

PURPOSE

To evaluate possible toxicity of intravitreal Kenalog (commercial triamcinolone acetonide) to the retina of albino rabbits.

METHODS

Forty-three albino rabbits were injected intravitreally with 0.1 mL of experimental solution to the right eye and 0.1 mL of saline to the left eye (control). Rabbits in Group A (n=28) were injected with 4 mg/0.1 mL of Kenalog suspension; rabbits in Group B (n=8) were injected with 0.1 mL of Kenalog vehicle; and rabbits in Group C (n=7) were injected with 4 mg/0.1 mL of triamcinolone acetonide. Rabbits were examined ophthalmoscopically and by electroretinogram (ERG) recordings before and at different time intervals after injection. At the end of follow-up, animals were killed and the retinas were prepared for light microscopy.

RESULTS

Thirty-eight rabbits completed 4 weeks of follow-up. Follow-up for 8 and 17 weeks was completed by 29 and 3 rabbits, respectively. Intravitreal commercial Kenalog or its vehicle alone caused approximately 50% reduction in the ERG b-wave amplitude at the end of follow-up. Pure triamcinolone acetonide caused only mild (up to 14%) reduction of the ERG b-wave amplitude. Histologic examination of retinas exposed to Kenalog or its vehicle showed severe damage to all retinal layers in areas close to the site of Kenalog injection.

CONCLUSIONS

Intravitreal injection of 4 mg Kenalog suspension is retinotoxic to albino rabbit eyes. The vehicle of Kenalog is probably the main cause of this toxicity.

A novel isoform of acetylcholinesterase exacerbates photoreceptors death after photic stress

PURPOSE

To study the involvement of stress-induced acetylcholinesterase (AChE) expression in light-induced retinal damage in albino rats.

METHODS

Adult albino rats were exposed for 24 hours to bright, damaging light. AChE expression was monitored by in situ hybridization, by histochemistry for AChE activity, and by immunocytochemistry. An orphan antisense agent (Monarsen; Ester Neurosciences, Ltd., Herzlia Pituach, Israel) was administered intraperitoneally to minimize light-induced AChE expression. The electroretinogram (ERG) was recorded to assess retinal function.

RESULTS

Twenty-four-hour exposure to bright light caused severe reduction in the ERG responses and augmented expression of mRNA for the "read-through" variant of AChE (AChE-R) in photoreceptor inner segments (IS), bipolar cells, and ganglion cells. AChE activity increased in IS. The expressed AChE protein was a novel variant, characterized by an extended N terminus (N-AChE). Systemic administration of the orphan antisense agent, Monarsen, reduced the photic induction of mRNA for AChE-R, and of the N-AChE protein. Rats exposed to bright, damaging light and treated daily with Monarsen exhibited larger ERG responses, relatively thicker outer nuclear layer (ONL), and more ONL nuclei than did rats exposed to the same damaging light but treated daily with saline.

CONCLUSIONS

The findings indicate that the photic-induced novel variant of AChE (N-AChE-R) may be causally involved with retinal light damage and suggest the use of RNA targeting for limiting such damage.

Posterior vitreous detachment induced by nattokinase (subtilisin NAT): a novel enzyme for pharmacologic vitreolysis

PURPOSE

To investigate the effects of intravitreal injection of nattokinase (subtilisin NAT), a serine protease that is produced by Bacillus subtilis (natto), for induction of posterior vitreous detachment (PVD).

METHODS

Different doses of nattokinase (1, 0.1, or 0.01 fibrin-degradation units [FU]) or physiologic saline as a control were injected into the vitreous cavity of rabbit eyes. Scanning electron microscopy was used to observe the retinal surfaces of four rabbit eyes per concentration. Histologic alterations were assessed by light microscopy, using four eyes from each group. Electroretinography (ERG) was performed to observe retinal function, ranging from 1 hour to 1 week after the nattokinase (1 or 0.1 FU) or saline solution administration, using four eyes from each group at each time point. Also, findings in all rabbits were monitored by slit lamp examination and by indirect ophthalmoscopy with a 20-D lens.

RESULTS

Scanning electron microscopy showed smooth retinal surfaces, indicating the occurrence of PVD at 30 minutes after intervention in all the experimental eyes injected with 0.1 or 1.0 FU nattokinase, but none of the control eyes. Light microscopy and ERG analysis showed no critical change even after the use of 0.1 FU nattokinase, an amount sufficient to induce PVD. However, toxicity in the forms of preretinal hemorrhage and ERG changes was noted with the higher dose (1 FU) of nattokinase.

CONCLUSIONS

The results suggested that nattokinase is a useful enzyme for pharmacologic vitreolysis because of its efficacy in inducing PVD.

Electrophysiologic and retinal penetration studies following intravitreal injection of bevacizumab (Avastin)

PURPOSE

Intravitreal bevacizumab (Avastin; Genentech Inc., San Francisco, CA) is a new treatment for age-related macular degeneration. The aim of this study was to evaluate retinal penetration and toxicity of bevacizumab.

METHODS

Ten albino rabbits were injected intravitreally with 0.1 mL (2.5 mg) of Avastin into one eye and 0.1 mL saline into the fellow eye. The electroretinogram (ERG) was recorded after 3 hours, 3 days, and 1, 2, and 4 weeks. The visual evoked potential (VEP) was recorded after 4 weeks. Confocal immunohistochemistry was used to assess retinal penetration.

RESULTS

The ERG responses of the control and experimental eyes were similar in amplitude and pattern throughout the follow-up period. The flash VEP responses of the experimental eyes were of normal pattern and amplitude and did not differ from those recorded by stimulation of the control eye alone. Full thickness retinal penetration was present at 24 hours and was essentially absent at 4 weeks.

CONCLUSIONS

Bevacizumab was found to be nontoxic to the retina of rabbits based on electrophysiologic studies. Full thickness retinal penetration may explain observed clinical effects of intravitreal bevacizumab. Although it is difficult to directly extrapolate to humans, our study supports the safe use of intravitreal bevacizumab injection.

NADPH diaphorase activity in the rat retina during the early stages of experimental diabetes

BACKGROUND

Nitric oxide (NO) plays an important physiological role in inter-cellular communication, but when produced in excess it can become toxic. Our goal was to evaluate possible involvement of NO in the development of retinopathy in diabetic rats.

METHODS

Diabetes was induced in male albino rats by intravenous injection of streptozotocin. Some of the normal and diabetic rats were raised with added L-arginine to increase in vivo NO synthesis, or with added L-NAME to inhibit the rate of in vivo NO synthesis. NADPH diaphorase histochemistry was conducted on retinal whole mounts and transverse sections at different time intervals after induction of diabetes. The electroretinogram (ERG) was recorded to assess retinal function.

RESULTS

After 6 weeks of diabetes, NADPH diaphorase amacrine cells in the diabetic retinas appeared abnormal in their morphology and the degree of staining was decreased in their processes. In contrast, NADPH diaphorase activity was augmented in Müller cells. Supplementing the rats' diet with L-arginine for 10 weeks slightly reduced NADPH diaphorase activity in amacrine cell in normal rats but had no effect on the diabetic rats. Adding L-NAME for 10 weeks did not alter NADPH diaphorase histochemistry in either normal or diabetic rats. The ERG responses were reduced by L-arginine supplementation in normal and diabetic rats, and were unaffected by adding L-NAME to the drinking water.

CONCLUSIONS

Our findings are consistent with the hypothesis that high glucose levels are deleterious to the rat retina and that excessive synthesis of NO may contribute to the development of diabetic retinopathy.

Early retinal damage in experimental diabetes: electroretinographical and morphological observations

A growing body of evidence indicates that impairment of retinal function precedes the earliest signs of vascular complications. The aim of this study was to follow the development of retinopathy both functionally and morphologically in a rat model of diabetes mellitus. Diabetes was induced in rats by intravenous injection of streptozotocin (STZ). Age-matched rats raised under similar conditions served as control. The electroretinogram (ERG) was recorded in order to assess retinal function. The expression of glial fibrillary acidic protein (GFAP) in Müller cells was used as a cellular marker for retinal damage. The ERG responses of the diabetic rats were reduced in amplitude compared to the responses recorded from the control rats as early as 2 weeks after onset of diabetes. The b-wave was more affected than the a-wave. GFAP expression in the diabetic retina did not differ from that in the control retina during the first 5 weeks of diabetes. GFAP was demonstrated only in astrocytes in the vitreo-retinal border. After 6-7 weeks of diabetes, GFAP expression in the retinas of the diabetic rats was also detected in the endfeet of the Müller cells. With the progression of diabetes, GFAP expression spreads throughout the entire length of the Müller cells. In the retinas from control rats, GFAP expression was limited to astrocytes and was not detected in Müller cells even at 40 weeks of follow-up. The observations indicate that the functional integrity of retinal cells is compromised already at short time intervals after onset of experimental diabetes in rats.

Retinal toxicity of gentamicin after subconjunctival injection performed adjacent to thinned sclera

OBJECTIVE

To investigate the potential toxicity to the retina of gentamicin injected near surgically thinned scleral areas in a rabbit model.

DESIGN

Experimental study.

METHODS

Scleral scraping to half thickness was performed in the superotemporal scleral area in both eyes of adult rabbits (n = 10). Gentamicin sulfate was injected subconjunctivally to the right eye and saline to the left eye, which always served as a control eye. Four weeks after the procedure, electroretinography (ERG) was performed to assess retinal function. Then, the eyes were enucleated and prepared for histologic evaluation of structural damage. In four eyes of two additional rabbits, vitreous gentamicin concentrations were measured using a fluorescence polarization assay.

MAIN OUTCOME MEASURES

Dark- and light-adapted ERG responses and histopathologic damage.

RESULTS

Dark- and light-adapted ERG responses in all rabbits were similar in the experimental and control eyes. Gentamicin levels were more than 10 microg/ml after subconjunctival injection of gentamicin with scraping and 0.29 microg/ml after subconjunctival injection of gentamicin with no scraping. Histopathologic examination revealed significant local damage to the photoreceptors adjacent to the area of scraping and subconjunctival injection. A significantly lesser degree of damage was seen if gentamicin was injected in pigmented rabbits or in albino rabbits, but only 4 weeks after scleral scraping.

CONCLUSIONS

Increased penetration of gentamicin through thinned sclera may lead to toxic levels of the drug in a localized area adjacent to the site of injection. These toxic effects are also influenced by the degree of pigmentation and acute inflammation.

NADPH diaphorase activity in the rabbit retina is modulated by glutamatergic pathways

NADPH diaphorase activity in the rabbit retina is modulated by the state of visual adaptation. In this study, we tested possible glutamatergic control of this phenomenon. Rabbits were injected intravitreally with agonists and antagonists of glutamate. After adaptation (3 hours) to either room light or darkness, the rabbits were killed and the retinae were prepared for NADPH diaphorase histochemistry. Kainic acid significantly reduced the number of NADPH diaphorase amacrine cells but augmented NADPH diaphorase activity in horizontal cells in both light- and dark-adapted animals. 6,7-Dinitroquinoxaline-2,3(1H,4H)-dione exerted no effect on amacrine cells but eliminated NADPH diaphorase activity in horizontal cells. 2-Amino-4-phosphono butyric acid did not affect NADPH diaphorase activity in horizontal cells but reduced the degree of staining in the neuronal processes of amacrine cells. MK-801 and N-methyl-D-aspartic acid (NMDA) had no effect on NADPH diaphorase activity in horizontal cells. However, MK-801 reduced staining in the neuronal processes of amacrine cells but not in their cell bodies. NMDA effects were expressed in a significant reduction in the number and size of amacrine cells that were NADPH diaphorase positive. These results indicate that activation of NADPH diaphorase in horizontal cells by darkness is mediated by the activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainic acid (KA)-type glutamate receptors. The ON pathway in the retina is probably involved in modulation of NADPH diaphorase in the neuronal processes of amacrine cells. Amacrine cells that are NADPH diaphorase positive contain NMDA-type and AMPA/KA-type receptors and are highly susceptible to NMDA and kainic acid toxicity.

Development of laser-induced retinal damage in the rabbit

BACKGROUND

Laser lesions may induce retinal damage that is larger than expected from the size of the coagulated area. This study was designed to follow the development of laser-induced reduction in retinal function and to correlate it with structural changes.

METHODS

Pigmented rabbits were treated in one eye with 225 argon laser lesions. The ERG responses were recorded at different times after treatment. The effect of the laser treatment upon the functional integrity of the retina was assessed from the ERG responses. Structural damage was examined by light microscopy.

RESULTS

Shortly (1-2 h) after laser treatment, the ERG responses were reduced by about 50%. ERG deficit continued to develop and reached a maximal level about 24 h after treatment. Thereafter, slow recovery was observed but permanent deficit, relative to the initial laser effect, was seen even 30 days after treatment. Histological observations indicated extensive serous retinal detachment between laser lesions that developed within 24 h after treatment. At 30 days post-treatment, lesioned areas were completely destroyed and heavily pigmented. The retina between lesions was attached to the pigment epithelium but exhibited different degrees of structural damage.

CONCLUSIONS

The immediate laser damage is confined to the coagulated areas while secondary functional damage develops within 24 h and probably reflects serous retinal detachment between lesions. The serous retinal detachment completely resolves with time but may induce permanent structural abnormalities in non-coagulated retinal areas that is reflected in a functional deficit larger than the initial laser effect.

NADPH diaphorase activity in mammalian retinas is modulated by the state of visual adaptation

NADPH diaphorase histochemistry is commonly used to identify cells containing nitric oxide synthase (NOS), the enzyme catalyzing the production of nitric oxide from L-arginine. NADPH diaphorase activity and NOS immunostaining was demonstrated in different cells of the vertebrate retina; photoreceptors, horizontal cells, amacrine cells, ganglion cells, and Müller cells. However, the physiological role of nitric oxide (NO) in the retina has yet to be elucidated. In this study, we tested the assumption that NADPH diaphorase activity in the retinas of rabbits and rats depended on the state of visual adaptation. In the rabbit, light adaptation enhanced NADPH diaphorase activity in amacrine cells and practically eliminated it in horizontal cells. Dark adaptation induced the opposite effects; the NADPH diaphorase activity was reduced in amacrine cells and enhanced in horizontal cells. Retinas from eyes that were injected intravitreally with L-glutamate exhibited a pattern of NADPH diaphorase activity that was similar to that seen in dark-adapted retinas. In rats, the NADPH diaphorase activity of amacrine and horizontal cells exhibited adaptation dependency similar to that of the rabbit retina. But, the most pronounced effect of dark adaptation in the rat's retina was an enhancement of NADPH diaphorase activity in Müller cells, especially of the endfoot region. Assuming that NADPH diaphorase activity is a marker for NOS, these findings suggest that NO production in the mammalian retina is modulated by the level of ambient illumination and support the notion that NO plays a physiological role in the retina.

Ocular pigmentation protects the rabbit retina from gentamicin-induced toxicity

PURPOSE

This study was designed to investigate the possibility that gentamicin-induced retinal toxicity is dependent on ocular pigmentation by comparing the effects of the drug on the functional and morphologic integrity of the retina in albino and pigmented rabbits.

METHODS

In each rabbit, a solution of gentamicin sulfate was injected into the vitreous of one eye, and saline was injected into the other eye. Retinal function was assessed by electroretinogram (ERG) at different time intervals after injection. Retinal structure was examined at the light microscopic level.

RESULTS

In albino and pigmented rabbits, functional retinal damage developed to a maximal level within the first week after gentamicin injection. Thereafter, gradual recovery could be seen in eyes that suffered less than 80% maximal reduction in the ERG b-wave. For each dose >0.1 mg studied, retinal damage was more severe in the albino rabbits than in the pigmented ones. The degree of damage was not affected by the level of ambient illumination, nor was it reduced by the administration of N-acetylcystein, a free radical scavenger, together with gentamicin.

CONCLUSIONS

Ocular pigmentation partially protects the rabbit retina from the toxic action of gentamicin. This protection probably reflects binding of the drug by the melanin, which thereby reduces the concentration of the free gentamicin. When the initial gentamicin-induced retinal damage is expressed in < 80% reduction in the ERG, substantial recovery may occur in both strains of rabbits.

The effects of lidocaine and bupivacaine on the rabbit retina

The toxic action of two commercial anesthetics, lidocaine and bupivacaine, on the functional and morphologic integrity of the retina was investigated in albino and pigmented rabbits. The experimental drug was injected into the vitreous of one eye, while saline solution was injected into the fellow eye. Retinal function was assessed from the electroretinogram and the visual evoked potential. Retinal structure was examined at the light microscopic level. Ten milligrams of lidocaine did not affect the electroretinogram and the visual evoked potential responses, though structural damage could be detected close to the site of injection. A lower dose of 5 mg did not produce any detectable physiologic or morphologic damage. The only dose of bupivacaine used, 0.5 mg, was not toxic to the albino and pigmented rabbit retinas, as assessed by the electroretinogram, visual evoked potential, and light microscopy. The results of this study demonstrate that lidocaine and bupivacaine are nontoxic to the rabbit retina at concentrations that are effective for retrobulbar anesthesia.

Drug-induced retinal toxicity in albino rabbits: the effects of imipenem and aztreonam

PURPOSE

To test the toxic action of two antibiotics, imipenem and aztreonam, on the functional and morphologic integrity of the albino rabbit retina.

METHODS

Two commercial drugs were used--Tienam, which contains imipenem, and Azactam, which contains aztreonam. Different doses of these drugs were injected intravitreally. Retinal function was assessed from the electroretinogram (ERG) and the visual evoked potential (VEP). Retinal structure was examined at the light microscopic level.

RESULTS

Imipenem did not affect the ERG and the VEP responses or the morphology of the retina up to a total injected dose of 0.98 mg (2 mg Tienam). Aztreonam was not toxic to the albino rabbit retina up to a total injected dose of 2.8 mg (5 mg of Azactam). Severe functional and morphologic retinal damage was seen when 10 mg of Azactam was injected. A similar degree of damage was seen when a dose of 5 mg L-arginine, an ingredient of Azactam, was injected into the vitreous.

CONCLUSIONS

Imipenem and aztreonam are nontoxic to the albino rabbit retina at concentrations that are 500-fold higher than their effective dose against bacterial infection. Azactam is highly toxic at high levels (more than 10 mg injected into the vitreous). Most of the toxicity could be explained by the L-arginine content of the drug.

The effects of myristyl gamma-picolinium chloride on the rabbit retina: morphologic observations

PURPOSE

This study was designed to localize the site of action of myristyl gamma-picolinium chloride (MGP) in the rabbit retina and to evaluate the extent of the structural damage induced by the drug.

METHODS

The structural damage was assessed at the light microscopic level in eyes treated with various concentrations of MGP at different time intervals after intravitreal injection of the drug. Glial fibrillary acidic protein (GFAP) immunoreactivity was tested in the same eyes and served as an index of retinal damage.

RESULTS

The rabbit retinas, examined about 1 mo after MGP injection, exhibited loss of photoreceptors and thinning of the retina in the regions close to the site of injection; remote retinal areas appeared morphologically intact or only slightly affected. Immunocytochemical analysis demonstrated the presence of GFAP in Müller (glial) cells throughout the entire retina. When the effects of MGP were examined at short time intervals (24 and 72 hr) after injection, severe morphologic damage in areas adjacent to the site of drug injection developed in parallel with the electroretinographic findings. However, GFAP could not be demonstrated.

CONCLUSIONS

MGP, the preservative used in Depo-Medrol (Upjohn, Kalamazoo, MI), is highly toxic to the rabbit retina.

The effects of Depo-Medrol preservative on the rabbit visual system

Periocular injections of corticosteroids play an important role in the management of various ophthalmologic diseases. The Depo-Medrol vehicle, injected into the vitreous, was shown to be toxic to the lens and to the retina when applied at double strength. The authors examined the effects of Depo-Medrol and one of the components of its vehicle, myristyl-gamma-picolinium chloride (MGP), on the functional integrity of the rabbit visual system. Visual function was assessed objectively from the electroretinogram (ERG) and the visual evoked potential (VEP). The experimental drugs were injected into the vitreous humor of one eye while saline was injected into the fellow eye for control. Depo-Medrol did not produce any measurable effects on the ERG or the VEP. When MGP solutions were injected in concentrations at least twice as large as that in the Depo-Medrol, significant reductions in the light- and dark-adapted ERG responses were seen. The effects of the drug on the ERG responses was seen as early as 3 days postinjection and developed to its maximal level within 1-2 weeks. No ERG recovery was seen over a period of more than 2 months. The VEP, elicited by applying light stimuli to the experimental eye, was characterized by low amplitude and delayed implicit time compared with the response obtained from the control eye.

Uridine diphosphoglucose dehydrogenase activity in normal and osteoarthritic human chondrocytes

The activity of uridine diphosphoglucose dehydrogenase (UDPGD), a key enzyme in the synthesis of proteoglycans was measured by a quantitative cytochemical method in normal and in osteoarthritic (OA) human cartilage. Normal adult chondrocytes showed low UDPGD activity, which was about half the activity of glucose-6-phosphate dehydrogenase of the same specimens. No significant increase in UDPGD activity was noted in OA chondrocytes. The lack of significantly enhanced UDPGD activity in OA indirectly agrees with studies showing normal 35S uptake in this disease and might explain in part the inability of chondrocytes to cope with continuous proteoglycan loss.

Photosystem II in Guard Cells of Vicia faba: Immunological Detection

Antibodies were raised against individual polypeptides of the oxygen-evolving photosystem II (PSII) complex from mesophyll chloroplasts of Vicia faba (Long Pod). These antibodies were used to probe immunologically for the presence of the main structural components of the PSII complex in guard cell chloroplasts, using both immunofluorescence microscopy and Western blotting. Immunofluorescence of epidermal peels with antibodies raised against the extrinsic 33 kilodalton polypeptide, as well as the 47 and the 44 kilodalton subunits and the light-harvesting chlorophyll a/b protein, resulted in intense fluorescence indicating the presence of these polypeptide components in guard cell chloroplasts. Results obtained with Western blot analysis showed that the relative amounts of the 33 kilodalton and light-harvesting complex protein polypeptides are between 60 and 80% of that found in mesophyll cells (on chlorophyll basis). These results provide evidence for the existence of structural components associated with PSII activity in guard cell similar to those of mesophyll chloroplasts.

Immunological evidence for the presence of ribulose bisphosphate carboxylase in guard cell chloroplasts

Ribulose bisphosphate carboxylase (Rubisco) has been found in Vicia faba L. guard cell chloroplasts by two immunological methods, using antibodies raised against highly purified subunits of ribulose bisphosphate carboxylase. Indirect cytoimmunofluorescence revealed binding of antibodies against both the small and the large subunits of ribulose bisphosphate carboxylase. Binding was observed only after partial digestion of guard cell walls by 4% Cellulysin to facilitate antibody penetration. After electrophoresis of a homogenate of guard cell protoplasts, the presence of both subunits was also revealed by immunolabeling technique. Positive response required the inhibition of proteolysis which appeared to be active upon homogenization.