Serous Retinal Detachment without Leakage on Fluorescein/Indocyanine Angiography in MEK Inhibitor-Associated Retinopathy.

The aim of this paper was to report the cases of 3 consecutive patients with mitogen-activated protein kinase kinase inhibitor (MEKi)-associated retinopathy with characteristic multiple serous retinal detachments (SRDs). A functional analysis of the retinal pigment epithelium was performed in 2 patients by electro-oculography (EOG). In all 3 patients, SRD lesions were observed in the posterior pole including the fovea of both eyes. Interestingly, neither obvious leakage in fluorescein/indocyanine angiography nor abnormal fundus autofluorescence was associated. SRDs and associated cystoid macular edema in one case rapidly resolved with the cessation of MEKi but recurred quickly after treatment resumption. In EOG tests, three of four eyes with multiple SRDs showed a marked decrease in the light-peak-to-dark-trough ratio (LP:DT ratio). The LP:DT ratio in EOG reflects the transepithelial potential of the retinal pigment epithelium, suggesting the involvement of disrupted tight junctions and impaired active transport of fluid/ions in MEKi-associated retinopathy. The latter may be the major cause of SRDs as we observed that fluid leakage in angiography was absent in the areas of the patients' SRDs.

Oct motif variants in Beckwith-Wiedemann syndrome patients disrupt maintenance of the hypomethylated state of the H19/IGF2 imprinting control region.

The methylation status of imprinting control center 1 (IC1) regulates the monoallelic transcription of H19 and Igf2 in mammalian cells. Several single nucleotide variants in Oct motifs within IC1 occur in patients with Beckwith-Wiedemann syndrome (BWS) who have hypermethylated maternal IC1. However, the importance of Oct motifs in the regulation of IC1 methylation status remains unclear. Here, we demonstrate that three variants found in BWS (BWS variants) suppress intensive induction of DNA demethylation, whereas consensus disruption of motifs unrelated to BWS only slightly affects the induction of demethylation. BWS variants reduce DNA demethylation levels and trigger the accumulation of DNA methylation downstream of the IC1 transgenes. Thus, the risk of IC1 hypermethylation is associated with inhibitory levels of Oct motif-dependent hypomethylation maintenance activities.

Urate transport function of rat sodium-dependent nucleobase transporter 1.

Sodium-dependent nucleobase transporter 1 (SNBT1) is a nucleobase-specific transporter identified in our recent study. In an attempt to search for its potential substrates other than nucleobases in this study, we could successfully find urate, a metabolic derivative of purine nucleobases, as a novel substrate, as indicated by its specific Na+ -dependent and saturable transport, with a Michaelis constant of 433 µmol/L, by rat SNBT1 (rSNBT1) stably expressed in Madin-Darby canine kidney II cells. However, urate uptake was observed only barely in the everted tissue sacs of the rat small intestine, in which rSNBT1 operates for nucleobase uptake. These findings suggested that urate undergoes a futile cycle, in which urate transported into epithelial cells is immediately effluxed back by urate efflux transporters, in the small intestine. In subsequent attempts to examine that possibility, such a futile urate cycle was demonstrated in the human embryonic kidney 293 cell line as a model cell system, where urate uptake induced by transiently introduced rSNBT1 was extensively reduced by the co-introduction of rat breast cancer resistance protein (rBCRP), a urate efflux transporter present in the small intestine. However, urate uptake was not raised in the presence of Ko143, a BCRP inhibitor, in the everted intestinal tissue sacs, suggesting that some other transporter might also be involved in urate efflux. The newly found urate transport function of SNBT1, together with the suggested futile urate cycle in the small intestine, should be of interest for its evolutional and biological implications, although SNBT1 is genetically deficient in humans.