Tracking Systemic and Ocular Vitamin A

Vitamin A in the form of 11-cis-retinaldehyde is the chromophore essential to vision. Thus, deficiencies in vitamin A necessitate the implementation of vitamin A supplementation. Moreover, some vitamin A is lost from the visual cycle due to random reactions that generate diretinaldehyde (bisretinoid) molecules; the latter are photoreactive and contribute to retinal disease. Here, we measured the systemic and ocular uptake of vitamin A along with bisretinoid as a function of vitamin A availability when supplied in the diet or by weekly i.p. injection in light- and dark-reared mice. Retinyl palmitate delivered as an i.p. bolus served to elevate plasma ROL but an associated increase in ocular 11-cisRAL was not observed in light- or dark-reared mice. In dark-reared mice, 11-cisRAL was more abundant when retinyl palmitate was provided in chow versus weekly i.p. injection; moreover, by the latter route, retinyl acetate was more effective. Conversely in dark-reared mice given retinyl palmitate by weekly i.p. injection versus chow, ocular atRAL was elevated. Liver atRE was elevated by increased retinyl palmitate in chow; the latter also favored elevated 11-cisRAL in dark-reared mice. In cyclic light-reared mice, ocular stores of atRE were increased by i.p. retinyl palmitate. With dark-rearing, there was no difference in bisretinoid (A2E) with retinyl palmitate in chow, nor by weekly i.p. injection; notably, bisretinoid levels were lower in cyclic light-reared mice due to photooxidative loss. In summary, light modulates the ocular retinoid, plasma atROL does not predict ocular levels of retinoid or bisretinoid and atRAL is elevated with sustained darkness.