Surrogate electroretinographic markers for assessing therapeutic efficacy in the retina

The Clinical Contribution of Full-Field Electroretinography and 8-Year Experiences of Application in a Tertiary Medical Center

Electroretinography (ERG) is an important and well-established examination for retinal and visual pathway diseases. This study reviewed the medical records of patients who received full-field ERG (ffERG) at a single medical center between 2012 and 2019, which was an 8-year experience in the clinical contribution of ERG. Based on the indication for scheduling ffERG and the final diagnosis, patients could be classified into six groups: ‘retinal dystrophies’, ‘other retinal or macular diseases’, ‘optic neuropathies’, ‘visual complaints’, ‘systemic diseases’, and ‘others’. A total of 1921 full-field electroretinograms (ffERGs) (1655 patients) were included. The average number of ffERGs performed per year was 262 and the number of annual ffERGs was constant. The ‘retinal dystrophies’ group accounted for 36.5% of the studied population, followed by the ‘other retinal or macular diseases’ group (20.2%). The most common systemic disease was central nervous system disease. The rates of abnormal ffERGs in the ‘systemic diseases’, ‘optic neuropathies’, and ‘visual complaints’ groups were 27.3%, 22.6%, and 10.1%, respectively (p < 0.001). Higher rates were found in patients <20 years old in the ‘systemic diseases’ and ‘optic neuropathies’ groups; epilepsy and optic nerve atrophy were the most common diagnoses, respectively. In brief, by quantifying the functional response in the retina, ffERG is indispensable for diagnosis and prognosis in ophthalmologic and multidisciplinary practice.

Effects of a monocarboxylate transport 1 inhibitor, AZD3965, on retinal and visual function in the rat

BACKGROUND AND PURPOSE

Inhibition of monocarboxylate transport 1 (MCT1) is of interest in targeting highly glycolytic tumours. However, MCT1 is expressed in retina, and so inhibition of MCT1 could affect retinal function.

EXPERIMENTAL APPROACH

AZD3965, an MCT1 inhibitor selected for clinical development, and two additional MCT1 inhibitors were evaluated for effects on visual acuity in albino (Han Wistar) rats. The effects of AZD3965 on visual acuity and electroretinography (ERG) were further investigated in pigmented (Long-Evans) rats, with dosing for up to 7 days.

KEY RESULTS

All three MCT1 inhibitors reduced visual acuity within 2 h of dosing, suggesting a class effect. The deficit caused by AZD3965 (1,000 mg·kg^-1 p.o. per day for 4 days) in Long Evans rats recovered to pre-dose levels 7 days after cessation of dosing. AZD3965 (50 to 1,000 mg·kg^-1 p.o.) reduced the amplitude of scotopic a- and b-waves, and photopic b-wave of the ERG in a dose-related fashion, within 2 h of dosing. The effects on the scotopic ERG had diminished by Day 7 of dosing, demonstrating partial restoration of function despite continued treatment. Seven days after cessation of dosing at the highest dose tested (1,000 mg·kg^-1 ), there was recovery of both scotopic a- and b- waves and, to a lesser extent, photopic b-wave. ERG was affected at lower plasma exposures than was visual function.

CONCLUSIONS AND IMPLICATIONS

This study clarifies the role of the MCT1 transporter in retinal function. The monitorability of the functional effects on the retina enabled safe clinical use of AZD3965.

Retinoprotective Effects of Bilberry Anthocyanins via Antioxidant, Anti-Inflammatory, and Anti-Apoptotic Mechanisms in a Visible Light-Induced Retinal Degeneration Model in Pigmented Rabbits

Excessive visible light exposure can induce damage to retinal cells and contribute to the development or progression of age-related macular degeneration. In this study we created a model of phototoxicity in pigmented rabbits. Furthermore, we investigated the protective effect of bilberry anthocyanin extract (BAE, Table A1) and explored the possible mechanisms of action in this model. The model of light-induced retinal damage was established by the pigmented rabbits exposed to light at 18,000 lx for 2 h, and they were sacrificed on day 7. After administration of BAE at dosages of 250 and 500 mg/kg/day, retinal dysfunction was significantly inhibited in terms of electroretinograms, and the decreased thicknesses of retinal outer nuclear layer and lengths of the outer segments of the photoreceptor cells were suppressed in rabbits with retinal degeneration. BAE attenuated the changes caused by light to certain apoptotic proteins (Bax, Bcl-2, and caspase-3). The extract increased the levels of superoxide dismutase, glutathione peroxidase, and catalase, as well as the total antioxidant capacity, but decreased the malondialdehyde level in the retinal cells. BAE inhibited the light-induced elevation in the levels of proinflammatory cytokines and angiogenic parameters (IL-1β and VEGF). Results showed that visible light-induced retinal degeneration model in pigmented rabbits was successfully established and BAE exhibited protective effects by increasing the antioxidant defense mechanisms, suppressing lipid peroxidation and proinflammatory cytokines, and inhibiting retinal cells apoptosis.

Effects of multiple doses of voriconazole on the vision of healthy volunteers: a double-blind, placebo-controlled study

PURPOSE

To investigate the effects, and their reversibility, of multiple oral voriconazole doses on a variety of visual tests in healthy male volunteers.

METHODS

Single-center, double-blind, randomized, placebo-controlled, parallel-group study in 36 volunteers who received voriconazole (n=18, 400 mg every 12 h on day 1, then 300 mg every 12 h for 27.5 days) or matched placebo (n=18). Electroretinograms (ERGs) and ophthalmological examinations were performed at screening, throughout the study and at follow-up.

RESULTS

Fifteen (83.3%) volunteers treated with voriconazole experienced ≥1 treatment-related visual adverse events (AEs); these included enhanced visual perceptions, blurred vision, color vision changes and photophobia. No serious AEs were reported. Voriconazole reduced from baseline scotopic maximal a- and b-wave amplitude, shortened implicit time and decreased oscillatory potential amplitude compared with placebo. Under photopic conditions, the 30-Hz flicker response amplitude was significantly reduced and was accompanied by a slight but nonsignificant prolongation of peak time. These effects did not progress in degree over the treatment period, and mean changes from baseline in ERG parameters were similar to placebo by day 43 (14 days after end of treatment). In the first week, color vision discrimination was impaired in the tritan axis, although this resolved by end of treatment and was similar to placebo by day 43. Mean deviation in the static visual field indicated increased sensitivity following voriconazole treatment, correlating with decreased amplitude in conjunction with shortened implicit time.

CONCLUSIONS

Effects of voriconazole on altered visual perception, ERG, color vision and static visual field thresholds are nonprogressive over a treatment period and reversible. It is hypothesized that voriconazole has a pharmacological effect on rod and cone pathways including a possible mechanism of disinhibition that reversibly puts the retina in a more light-adapted state and leads to increased relative contrast sensitivity.

Identification of anthocyanin components of wild Chinese blueberries and amelioration of light-induced retinal damage in pigmented rabbit using whole berries

Studies suggest that the consumption of berry fruits rich in anthocyanins may have beneficial effects on improving visual function. This study determined the total polyphenol and total anthocyanin contents in wild Chinese blueberries using the Folin-Ciocalteu reagent method and a pH differential method. Anthocyanin composition and quantity were characterized by high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry coupled with mass selective detection. Total polyphenol and anthocyanin contents were 602.9 ± 9.2 and 177.8 ± 8.3 mg/100 g, respectively. Seventeen anthocyanins were discovered, and only 13 were tentatively identified in the wild blueberries. Anthocyanins of malvidin glycosylated with hexose or pentose accounted for >46% of total anthocyanin content. Furthermore, the effect of whole blueberries on retinal damage in pigmented rabbits upon light exposure was investigated, and the retinal functions were evaluated by electroretinogram (ERG). Pigmented rabbits were chosen for this experiment because of their large eyes, which facilitated the operative procedure and observation, and the similarity of their eyes to the human eye structure. Light-induced retinal damage was induced by exposure to white light at 15000 ± 1000 lx for 2 h. Feeding the rabbits with blueberries at a dosage of 1.2 or 4.9 g/kg/day for 4 weeks prior to light exposure effectively reduced photodamage to the retinas. This study adds to the growing body of data supporting the bioactivity of blueberries in improving mammal vision.

Safety of recombinant adeno-associated virus type 2-RPE65 vector delivered by ocular subretinal injection

AAV2 delivery of the RPE65 gene to the retina of blind RPE65-deficient animals restores vision. This strategy is being considered for human trials in RPE65-associated Leber congenital amaurosis (LCA), but toxicity and dose efficacy have not been defined. We studied ocular delivery of AAV-2/2.RPE65 in RPE65-mutant dogs. There was no systemic toxicity. Ocular examinations showed mild or moderate inflammation that resolved over 3 months. Retinal histopathology indicated that traumatic lesions from the injection were common, but thinning within the injection region occurred only at the two highest vector doses. Biodistribution studies at 3 months postinjection showed no vector in optic nerve or visual centers in the brain and only isolated non-dose-related detection in other organs. We also performed biodistribution studies in normal rats at about 2 weeks and 2 months postinjection and vector was not widespread outside the injected eye. Dose-response results in RPE65-mutant dogs indicated that the highest 1.5-log unit range of vector doses proved efficacious. The efficacy and toxicity limits defined in this study lead to suggestions for the design of a subretinal AAV-2/2.RPE65 human trial of RPE65-associated LCA.