Light-induced Damage in the Retina: Differential Effects of Dimethylthiourea on Photoreceptor Survival, Apoptosis and DNA Oxidation

Abstract

In the rat, photoreceptor cell death from exposure to intense visible light can be prevented by prior treatment with antioxidants. In this study we subjected albino rats raised in dim cyclic light and rats made more susceptible to light damage by rearing in darkness to exposures of green light that led to similar losses of photoreceptor cells. Rhodopsin and photoreceptor DNA, indicators of the number of surviving photoreceptor cells, were determined at various times over a period of 14 days after light exposure. Fragmentation of DNA was determined over a similar time course by neutral and alkaline agarose gel electrophoresis. Apoptosis in retinal DNA was measured by quantitating the appearance of 180 base pair (bp) nucleosomal fragments. Oxidation of DNA was measured by electrochemical detection of the nucleoside 8-hydroxydeoxyguanosine (8-OHdG) after separation by high-performance chromatography. For albino rats reared in dim cyclic light, 24 h of intense light exposure resulted in the loss of 50% rhodopsin and photoreceptor cell DNA. In dark-reared rats, the losses were 40%, respectively, after only 3 h of intense light treatment. In both cases pretreatment with the antioxidant dimethylthiourea (DMTU) prevented rhodopsin and photoreceptor cell DNA loss. The kinetics of the light-induced apoptosis depended markedly on the rearing environment of the rats. The DNA ladders appeared within 12 h of the onset of intense light in the rats reared in dim cyclic light. In these rats the 180 bp fragment was at two-thirds of its maximum intensity immediately after 24 h of light exposure and reached the maximum 12 h later. Dimethylthiourea partially inhibited ladder formation in rats reared in dim cyclic light and delayed the time of appearance of the 180 bp maximum by 6 h. By contrast, in rats reared in darkness the 180 bp fragment was undetected immediately after 3 h of light exposure and reached its maximum 2 days later. Pretreatment with DMTU completely eliminated DNA ladders in these rats. Alkaline gel electrophoresis revealed a pattern of single-strand DNA breaks, with relatively high molecular weight fragments, 6 h after light exposure of dark-reared rats. Single-strand DNA breaks in cyclic light rats corresponded with the onset of apoptotic ladders, but peak values preceded by 12 h the peak of DNA ladder formation. The quantity of 8-OHdG in retinal DNA remained close to control values in all samples with the exception of a peak of twice the control value 18 h after light exposure in the dark-reared rats and a value 60% higher 16 days after exposure in cyclic light animals. Dimethylthiourea had no effect on the amount of oxidized purine in any of the samples. The differences between dark-reared rats and rats reared in dim cyclic light in the kinetics of DNA fragmentation and in their response to treatment with DMTU is consistent with previous observations of fundamental differences in retinal cell physiology in these animals. In dim light-reared rats, the pathway to apoptosis may be qualitatively different from the pa...

Light-induced exacerbation of retinal degeneration in a rat model of Smith–Lemli–Opitz syndrome

“…AU). The sparing effect of DMTU observed in these experiments was even greater than that previously reported for normal albino rats treated similarly (see Organisciak et al, 1999).…”

“…Intense light exposure (retinal light damage paradigm) was performed essentially as described in detail previously (Organisciak et al, 1996(Organisciak et al, , 1999Vaughan et al, 2003). After 20-24 hr of dark adaptation, control and AY9944-treated animals were light-exposed, either at P28 or P37 (when AY9944-treated animals show little sign of retinal degeneration; Fliesler et al, 1999).…”

“…Unexposed rats remained in darkness for the same 24 hr period. A subset of AY9944-treated and control rats was given subdermal aqueous injections of the synthetic antioxidant dimethylthiourea (DMTU, Sigma-Aldrich; 500 mg/kg) at 24 hr prior, and again at 1 hr prior, to the 24 hr of intense light exposure or continued darkness (Lam et al, 1990;Organisciak et al, 1999). All rats were allowed 2 weeks recovery in dim cyclic light after exposure prior to ERG recording and sacrifice, to permit clearance of dead photoreceptors (if any) from the outer nuclear layer (ONL).…”

The association between macular pigment optical density and CFH, ARMS2, C2/BF, and C3 genotype

“…Furthermore, MP is thought to preserve foveal S-cone sensitivity, protecting it from shortwavelength blue light damage in humans (Haegerstrom-Portnoy, 1988). It has also been shown that the administration of antioxidants can prevent light-induced retinal damage in rat retinas (Organisciak et al, 1999). More recently, dietary supplementation with L in mice has been reported to suppress laser-induced CNV formation, and to inhibit the associated inflammatory and angiogenic molecules related to CNV pathogenesis (Izumi-Nagai et al, 2007).…”

Lipid hydroperoxide formation in the retina: correlation with retinal degeneration and light damage in a rat model of Smith–Lemli–Opitz syndrome

“…The SLOS rat model was produced as previously described (Fliesler et al, 2004), by treatment of Sprague Dawley (albino) rats with AY9944, a selective inhibitor of 3β-hydroxysterol-Δ 7 -reductase (Dvornik et al, 1963;Givner and Dvornik, 1965 Inc.) upon weaning; rats were provided water, ad lib, and were maintained in dim cyclic light (20-40 lux, 12 hr light-12 hr dark) at 22-25 °C, unless otherwise stated. The retinal light damage paradigm was performed essentially as previously described (Organisciak et al, 1996(Organisciak et al, , 1999Vaughan et al, 2003Vaughan et al, , 2005. Rats (6-wk postnatal age, N=4 per group) were darkadapted overnight, and then exposed for 24 hr to intense green light (1700 lux, 490-580 nm) in a temperature-controlled, Plexiglass chamber (kindly provided by D.T.…”