β-alanine supplementation induces taurine depletion and causes alterations of the retinal nerve fiber layer and axonal transport by retinal ganglion cells

Abstract

To study the effect of taurine depletion induced by β-alanine supplementation in the retinal nerve fiber layer (RNFL), and retinal ganglion cell (RGC) survival and axonal transport. Albino Sprague-Dawley rats were divided into two groups: one group received β-alanine supplementation (3%) in the drinking water during 2 months to induce taurine depletion, and the other group received regular water. After one month, half of the rats from each group were exposed to light. Retinas were analyzed in-vivo using Spectral-Domain Optical Coherence Tomography (SD-OCT). Prior to processing, RGCs were retrogradely traced with fluorogold (FG) applied to both superior colliculi, to assess the state of their retrograde axonal transport. Retinas were dissected as wholemounts, surviving RGCs were immunoidentified with Brn3a, and the RNFL with phosphorylated high-molecular-weight subunit of the neurofilament triplet (pNFH) antibodies. β-alanine supplementation decreases significantly taurine plasma levels and causes a significant reduction of the RNFL thickness that is increased after light exposure. An abnormal pNFH immunoreactivity in some RGC bodies, their proximal dendrites and axons, and a further diminution of the mean number of FG-traced RGCs compared with Brn3a⁺RGCs, indicate that their retrograde axonal transport is affected. In conclusion, taurine depletion causes RGC loss and axonal transport impairment. Finally, our results suggest that care should be taken when ingesting β-alanine supplements due to the limited understanding of their potential adverse effects.

Keywords: Axonal transport; Light; Phototoxicity; Retinal degeneration; Retinal ganglion cells; Taurine.