Taurine and Zinc Modulate Outgrowth from Goldfish Retinal Explants

Abstract

Taurine and zinc, highly concentrated in the retina, possess similar properties in this structure, such as neuro-protection, membrane stabilization, influencing regeneration, and modulating development, maybe by acting in parallel or as interacting agents. We previously demonstrated that there are some correlations between taurine and zinc levels in hippocampus, dentate gyrus and retina of the developing rat. In the present study we evaluate the possible effects of taurine and zinc on outgrowth from goldfish retinal explants. The optic nerve was crushed 10 days before plating and culturing retinal explants in Leibovitz medium with 10% fetal calf serum and gentamicin. Neurites were measured with SigmaScanPro after 5 days in culture. Taurine (HPLC) and zinc (ICP) concentrations were determined in the retina between 1 and 180 days after crushing the optic nerve. Zinc sulfate (0.01-100 microM), N,N, N',N'-tetrakis (pyridylmethyl) ethylenediamine (TPEN, 0.1-5 nM) and diethylenetriamine penta-acetic acid (DTPA, 10-300 microM), intracellular and extracellular zinc chelators, respectively, were added to the medium. TPEN was also injected intraocular (0.1 nM). Combinations of them were added with taurine (1-16 mM). Taurine concentrations were elevated in the retina 72 h after the crush, but were normalized by 180 days, those of zinc increased at 24 h, preceding the increase of taurine. The axonal transport of [3H]taurine from the optic tectum to the retina was not affected in fish with or without crush of the optic nerve at early periods after the injection, indicating an increase of it post-lesion. Zinc sulfate produced a bell-shaped concentration dependency on in vitro outgrowth, with stimulation at 0.05 microM, and inhibition at higher levels, also increased the effect of 4 mM taurine at 0.02 microM, but diminished it at higher concentrations in the medium. TPEN decreased outgrowth at 1 nM, but not at 0.5 nM, although the simultaneous presence of 4 mM taurine and 0.5 nM TPEN decreased outgrowth respecting the stimulation by taurine alone. The intraocular administration of TPEN decreased outgrowth in vitro, an effect counteracted by the addition of 4 mM taurine to the culture medium. DTPA decreased outgrowth from 10 microM in the medium. The present results indicate that an optimal zinc concentration is necessary for outgrowth of goldfish retinal explants and that, in zinc deficient retina, taurine could stimulate outgrowth. In addition, the observations of variations in tissue concentrations and of the effects of intraocular administration of TPEN indicate that these effects could occur in vivo.

Effects of zinc ex vivo on taurine uptake in goldfish retinal cells

“…The trophic effect of taurine is inhibited by µM concentrations of zinc in cultures of goldfish retinal explants [16]. In addition, taurine does not counteract the inhibitory effect of 1 µM zinc [16], which may be due to inhibition of taurine transport.…”

“…The neuroprotective effect of low concentrations of zinc in the brain has been attributed to its antioxidant function and to the fact that zinc is an important modulator of excitatory synaptic transmission [7,15]. Zinc occurrence in cultures of goldfish retinal fragments at a concentration equal to or greater than 0.06 µM in the presence of taurine reduces the amino acid trophic effect, which could be related to the interaction between both in the membranes or to the influence of zinc on taurine transport [16]. It has been demonstrated that micromolar concentrations of zinc modulate the activity of voltage-dependent calcium channels, of receptors and of neurotransmitter transporters [17-20].…”

Complementary research models and methods to study axonal regeneration in the vertebrate retinofugal system

“…Likewise, porcine retinal explants are mostly used to analyze neuroprotection and cell survival, rather than neurite outgrowth MartinezFernandez;de la Camara et al 2014;Taylor et al 2014;Bell et al 2016). Regarding anamniote models, retinal explants harvested from goldfish or zebrafish have also been used to test the putative effect of both intrinsic and extrinsic factors on RGC outgrowth/regeneration, albeit to a more limited extend (Nusetti et al 2005;Veldman et al 2007Veldman et al , 2010Cubillan et al 2012;Ou et al 2012;Ogai et al 2014). To culture fish retinal explants, retinas are chopped into small squares and transferred to poly-L-lysine-coated well plates.…”

Effect of Taurine on Brain 8-hydroxydeoxyguanosine and 3-nitrotyrosine Levels in Endotoxemia

“…Measurement of taurine concentrations was accomplished by using the HPLC method described by McMahon et al [22]. Tissue homogenate preparation was made according to Nusetti et al [24]. In brief, 100 mg whole brain sample was homogenized in 0.1 N perchloric acid and centrifuged for 10 min at 6.000 g and 4°C.…”