Vitamin A and interstitial retinol-binding protein in an eye with recessive retinitis pigmentosa

The composition and amount of vitamin A stored in the retinal pigment epithelium and choroid (RPE-Ch) was evaluated in postmortem donor eyes from a patient with retinitis pigmentosa that was probably inherited by an autosomal recessive mode. Additionally, the soluble proteins in the neural retina and RPE-Ch cytosols and interphotoreceptor matrix were examined collectively for the presence of interstitial retinol-binding protein (IRBP). Although there was depletion of the amount of vitamin A stored in the RPE, this was commensurate with the histopathologic findings on the RPE extent and thickness. No evidence was found for an accumulation of free retinol. Nearly all of the vitamin A stored in the RPE was esterified. As in normal eyes, the retinyl esters consisted mainly of palmitate mixed with a small proportion of stearate. Eleven-cis retinyl esters were present, although their proportion was lower than that reported for normals. IRBP could not be detected in stained gels of the soluble proteins, or by autoradiography of these gels after treatment with 125I-concanavalin A. These findings suggest that depletion of stored vitamin A, accumulation of free retinol, or deficiency of 11-cis isomer are unlikely to be causative factors in the retinal degeneration examined here. Although the depletion of IRBP seen at this advanced stage might be secondary to the advanced loss of photoreceptors, the authors cannot rule out the possibility that a relative deficiency or abnormality in this protein at earlier disease stages may contribute to the pathogenesis of retinitis pigmentosa.