在上个世纪,确定了维生素A,其中包括营养相关的维生素A1/维生素原A1,以及维生素A2途径的概念。全球范围内,营养指南侧重于维生素A1,仅基于维生素A的简化建议和计算。维生素A/维生素原A术语描述了维生素A作为11-顺式视网膜的前体,视觉色素的发色团,以及视黄酸,是核激素受体视黄酸受体(RARs)α的配体,β和γ。全反式维甲酸被最终证明是内源性RAR配体,而其异构体9-顺式视黄酸的概念,作为类维生素A-X受体(RXRs)的内源性配体,仍然没有定论。最近,9-顺式-13,14-二氢视黄酸被最终报道为内源性RXR配体,并在2018年提出了一种直接的营养前体,并得到了鲁尔的进一步证实,2021年的Krezel和deLera。这进一步称为维生素A5/X/维生素原A5/X。在这次审查中,一个新的维生素A5/X/维生素原A5/X概念与维生素A(1)/维生素A(1)概念并行概念化,用于每日饮食摄入量和饮食指南。重点关注维生素A5/X的生理和营养相关性的现有国家和国际法规。本综述的目的是总结现有证据,并强调有关维生素A5/X的知识差距,基于新的和旧的研究和提出的未来方向,以及刺激和提出适应的营养法规。
In the last century, vitamin A was identified that included the nutritional relevant vitamin A1 / provitamin A1, as well as the vitamin A2 pathway concept. Globally, nutritional
guidelines have focused on vitamin A1 with simplified recommendations and calculations based solely on vitamin A. The vitamin A / provitamin A terminology described vitamin A with respect to acting as a precursor of 11-cis-retinal, the chromophore of the visual pigment, as well as retinoic acid(s), being ligand(s) of the nuclear hormone receptors retinoic acid receptors (RARs) α, β and γ. All-trans-retinoic acid was conclusively shown to be the endogenous RAR ligand, while the concept of its isomer 9-cis-retinoic acid, being \"the\" endogenous ligand of the retinoid-X receptors (RXRs), remained inconclusive. Recently, 9-cis-13,14-dihydroretinoic acid was conclusively reported as an endogenous RXR ligand, and a direct nutritional precursor was postulated in 2018 and further confirmed by Rühl, Krezel and de Lera in 2021. This was further termed vitamin A5/X / provitamin A5/X. In this review, a new vitamin A5/X / provitamin A5/X concept is conceptualized in parallel to the vitamin A(1) / provitamin A(1) concept for daily dietary intake and towards dietary
guidelines, with a focus on the existing national and international regulations for the physiological and nutritional relevance of vitamin A5/X. The aim of this review is to summarize available evidence and to emphasize gaps of knowledge regarding vitamin A5/X, based on new and older studies and proposed future directions as well as to stimulate and propose adapted nutritional regulations.