Drugs and the retina

OCT retinal angiography features in patients with rheumatoid arthritis: A pilot study

PURPOSE

To evaluate the superficial (SCP) and deep retinal capillary plexus (DCP) by mean of optical coherence tomography angiography (OCTA) in treatment-naïve patients affected by rheumatoid arthritis (RA).

METHODS

Between March 2019 and January 2020, patients with recent diagnosis of "definite RA" based on 2010 Rheumatoid Arthritis Classification Criteria were included in a Prospective, observational single center case-control study carried out at G.B. Bietti Foundation. Data were compared with those of 16 healthy age- and sex-matched subjects. Values of the vessel density (VD) of SCP and DCP, central foveal thickness (CFT), foveal avascular zone (FAZ) were collected by mean of OCTA. Main outcome measure was the VD alteration of SCP and DCP in treatment-naïve RA-patients.

RESULTS

No difference in age, sex-distribution, best-corrected visual acuity, CFT was registered between the two groups. OCTA data analysis showed in RA-patients a statistically significant reduction in the VD in the mean global area, inner ring, especially in the superior quadrant of the SCP. A trend of VD reduction was also registered in temporal, nasal, and inferior quadrants, respectively, although it did not reach a statistically significant value. Assessment of VD of DCP and FAZ area did not evidence any difference among the groups.

CONCLUSIONS

OCTA allows to highlight the vascular remodeling of the retinal microcirculation in RA-patients, even in early stages of the disease, demonstrating a reduction of VD. Outcomes of the current investigation can provide new insight in the pathogenetic mechanism of RA and extend the potential applications of this diagnostic tool.

Evaluation of a convenient method of assessing rodent visual function in safety pharmacology studies: effects of sodium iodate on visual acuity and retinal morphology in albino and pigmented rats and mice

INTRODUCTION

We have evaluated the ability of a semi-automated, optomotor reflex method to assess drug-induced visual dysfunction, in albino and pigmented rats and mice.

METHODS

Male Han Wistar (HW) and Long Evans (LE) rats and mice (CD-1 and C57BL/6) were tested in a chamber formed by 4 computer monitors displaying a rotating vertical grating, to elicit head-tracking movements. The highest visible grating frequency was taken as the threshold of visual acuity, in cycles per degree (c/d). Animals received an intravenous infusion of either sodium iodate (50mg/kg) or 0.9% w/v NaCl (aq). They were tested 2h later, then re-tested daily for a further 3 days. The time course of the effect was assessed in HW rats over a 6-week period, including electron microscopy, and immunohistochemical analysis of markers of injury and repair in the retina.

RESULTS

Baseline visual acuities for HW and LE rats were 0.355 ± 0.007 and 0.530 ± 0.004 c/d, respectively, and 0.296 ± 0.003 c/d and 0.370 ± 0.001 c/d for CD-1 and C57BL/6 mice, respectively (n=10 for each). In HW rats there was a dramatic loss of visual acuity 2h after administration of sodium iodate (0.021 ± 0.021 c/d; P<0.001). Less dramatic decreases in visual acuity were seen in LE rats and in the two mouse strains. In HW rats, visual acuity was restored after 4 weeks. This paralleled the histopathological recovery of the peripheral retina, whereas the central retina did not recover.

DISCUSSION

The method proved to be very convenient, and the stability of visual acuity in vehicle control rats over a 6-week period also demonstrated its suitability for inclusion in long-term toxicity studies. Both albino and pigmented mice and rats are suitable for assessment of retinotoxicity using this method, but albino rats are the most sensitive to sodium iodate.

A behavioural operant discrimination model for assessment and pharmacological manipulation of visual function in rats

A large number of commercially available drugs are known to cause visual side effects in humans. Therefore, it would be advantageous to screen for alterations in visual function at a pre-clinical stage. Available methods, however, lack control for motivational and motoric side effects. The aim of the present study was therefore to develop a behavioural test to detect and quantify drug-induced visual side effects while simultaneously controlling for other side effects. We here present a novel model based on operant conditioning methodology with a food rewarded two-choice design to assess visual acuity and contrast sensitivity in rats. Rats were trained to discriminate between computer-generated sine-wave gratings and homogenous grey stimuli of equal luminance. They were subsequently tested with novel stimuli differing to training stimuli according to either spatial frequency or contrast. Finally, we tested how visual acuity was affected by oral administration of quinine HCl, a compound known to affect visual function in man. The rats learned to discriminate visual stimuli within 4-5weeks of twice daily training. A training procedure with moving stimuli achieved faster learning than with static stimuli. The visual detection threshold for discrimination of grating patterns decreased as a function of the contrast level, ranging from a spatial frequency of 0.8cycles/degree (c/d) at 100% contrast to 0.2c/d at 12.5%. Administration of quinine HCl was shown to affect the visual acuity threshold in a dose- and time dependent manner. In addition, response rate was affected by quinine administration but temporally isolated from the attenuation of visual acuity demonstrating that this model can separate the visual effects from motoric and motivational side effects.

Epilepsy pharmacogenetics

Large interindividual variation in efficacy and adverse effects of anti-epileptic therapy presents opportunities and challenges in pharmacogenomics. Although the first true association of genetic polymorphism in drug-metabolizing enzymes with anti-epileptic drug dose was reported 10 years ago, most of the findings have had little impact on clinical practice so far. Most studies performed to date examined candidate genes and were focused on candidate gene selection. Genome-wide association and whole-genome sequencing technologies empower hypothesis-free comprehensive screening of genetic variation across the genome and now the main challenge remaining is to select and study clinically relevant phenotypes suitable for genetic studies. Here we review the current state of epilepsy pharmacogenetics focusing on phenotyping questions and discuss what characteristics we need to study to get answers.

CNS adverse events associated with antiepileptic drugs

A variety of newer antiepileptic drugs (AEDs) are now available for treating patients with epilepsy in addition to the 'conventional' drugs that have been available throughout a large part of the last century. Since these drugs act to suppress the pathological neuronal hyperexcitability that constitutes the final substrate in many seizure disorders, it is not surprising that they are prone to causing adverse reactions that affect the CNS.Information on adverse effects of the older AEDs has been mainly observational. Equally, whilst the newer drugs have been more systematically studied, their long-term adverse effects are not clearly known. This is illustrated by the relatively late emergence of the knowledge of visual field constriction in the case of vigabatrin, which only became known after several hundred thousand patient-years of use. However, older drugs continue to be studied and there has been more recent comment on the possible effect of valproate (valproic acid) on cognition following exposure to this drug in utero.With most AEDs, there are mainly dose-related adverse effects that could be considered generic, such as sedation, drowsiness, incoordination, nausea and fatigue. Careful dose titration with small initial doses can reduce the likelihood of these adverse effects occurring. Adverse effects such as paraesthesiae are more commonly reported with drugs such as topiramate and zonisamide that have carbonic anhydrase activity. Weight loss and anorexia can also be peculiar to these drugs. Neuropsychiatric adverse effects are reported with a variety of AEDs and may not be dose related. Some drugs, such as carbamazepine when used to treat primary generalized epilepsy, can exacerbate certain seizure types. Rare adverse effects such as hyperammonaemia with valproate are drug specific. There are relatively very few head-to-head comparisons of AEDs and limited information is available in this regard.In this review, we discuss the available literature and provide a comprehensive summary of adverse drug reactions of AEDs affecting the CNS.

Antiepileptic drugs and visual function

Antiepileptic drugs are known to result in visual disturbances. A number of antiepileptic drugs have recently been reported to result in various abnormalities of vision, particularly deficiencies in visual fields and color vision. Moreover, there has been a marked improvement in the diagnosis and understanding of the pathophysiology of visual disturbance. This review collects evidence for visual adverse effects induced by the older antiepileptic drugs (barbiturates, benzodiazepine, carbamazepine, valproic acid, ethosuximide, and phenytoin) and the newer ones (vigabatrin, topiramate, tiagabine, levetiracetam, lamotrigine, gabapentin, felbamate, and oxcarbazepine).

Vascular endothelium-selective gene induction by Tie2 promoter/enhancer in the brain and retina of a transgenic rat

PURPOSE

To produce a transgenic rat harboring the Tie2 promoter/enhancer linked green fluorescence protein (GFP) gene and investigate the blood-brain barrier (BBB)- and inner blood-retinal barrier (iBRB)-selective GFP expression in the brain and retina.

METHODS

Transgenic rats were produced by the microinjection of mouse Tie2/GFP gene into fertilized oocytes of Wistar rats. The expression of GFP was observed in tissue slices by confocal microscopy.

RESULTS

One of the obtained transgenic lines showed intense GFP expression in vascular endothelial cells throughout the brain. After double immunostaining with glucose transporter 1, the GFP was found to be localized in the cytoplasmic compartment of brain capillary endothelial cells. In contrast, no fluorescence was observed in neural cells. In the retina of transgenic rats, intense GFP expression was detected in retinal capillary endothelial cells. No fluorescence was detected in other cells. In kidney and liver, GFP expression was detected in vascular endothelial cells, whereas the expressed region was limited.

CONCLUSIONS

Mouse Tie2 promoter/enhancer has the ability to induce gene expression selectively in vascular endothelial cells in the brain and retina of transgenic rats.

Advances in epilepsy

Advances in understanding of both the causes and consequences of epilepsy have been paralleled by a number of recent reports and clinical guidelines highlighting the complexities involved in both diagnosing and treating epilepsy. We review recent developments, including comments on the evolution of clinical guidelines, anti-epileptic drugs, epilepsy surgery and new treatment approaches in development. Epilepsy genetics and emerging evidence on mechanisms of drug resistance in epilepsy will also be discussed. Issues with respect to pregnancy and epilepsy are considered, together with more recently identified dilemmas including bone health in epilepsy and whether seizures themselves cause brain damage. Imaging in epilepsy has recently been reviewed elsewhere, and will not be discussed.