Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
Department of Genetics, Genomics, Bioinformatics and Informatics Institute, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
Biol Rev Camb Philos Soc. 2024 Oct;99(5):1772-1790. doi: 10.1111/brv.13091. Epub 2024 Apr 30.
Melatonin, a product of tryptophan metabolism via serotonin, is a molecule with an indole backbone that is widely produced by bacteria, unicellular eukaryotic organisms, plants, fungi and all animal taxa. Aside from its role in the regulation of circadian rhythms, it has diverse biological actions including regulation of cytoprotective responses and other functions crucial for survival across different species. The latter properties are also shared by its metabolites including kynuric products generated by reactive oxygen species or phototransfomation induced by ultraviolet radiation. Vitamins D and related photoproducts originate from phototransformation of ∆5,7 sterols, of which 7-dehydrocholesterol and ergosterol are examples. Their ∆5,7 bonds in the B ring absorb solar ultraviolet radiation [290-315 nm, ultraviolet B (UVB) radiation] resulting in B ring opening to produce previtamin D, also referred to as a secosteroid. Once formed, previtamin D can either undergo thermal-induced isomerization to vitamin D or absorb UVB radiation to be transformed into photoproducts including lumisterol and tachysterol. Vitamin D, as well as the previtamin D photoproducts lumisterol and tachysterol, are hydroxylated by cyochrome P450 (CYP) enzymes to produce biologically active hydroxyderivatives. The best known of these is 1,25-dihydroxyvitamin D (1,25(OH)D) for which the major function in vertebrates is regulation of calcium and phosphorus metabolism. Herein we review data on melatonin production and metabolism and discuss their functions in insects. We discuss production of previtamin D and vitamin D, and their photoproducts in fungi, plants and insects, as well as mechanisms for their enzymatic activation and suggest possible biological functions for them in these groups of organisms. For the detection of these secosteroids and their precursors and photoderivatives, as well as melatonin metabolites, we focus on honey produced by bees and on body extracts of Drosophila melanogaster. Common biological functions for melatonin derivatives and secosteroids such as cytoprotective and photoprotective actions in insects are discussed. We provide hypotheses for the photoproduction of other secosteroids and of kynuric metabolites of melatonin, based on the known photobiology of ∆5,7 sterols and of the indole ring, respectively. We also offer possible mechanisms of actions for these unique molecules and summarise differences and similarities of melatoninergic and secosteroidogenic pathways in diverse organisms including insects.
褪黑素是色氨酸通过血清素代谢产生的产物，是一种具有吲哚骨架的分子，广泛存在于细菌、单细胞真核生物、植物、真菌和所有动物中。除了在调节昼夜节律方面的作用外，它还具有多种生物学作用，包括调节细胞保护反应和其他对不同物种生存至关重要的功能。其代谢产物如活性氧或紫外线诱导的光转化产生的犬尿酸产物也具有这些特性。维生素 D 和相关的光产物来源于 ∆5,7 甾体的光转化，其中 7-脱氢胆固醇和麦角固醇就是例子。它们 B 环中的 ∆5,7 键吸收太阳紫外线辐射[290-315nm，紫外线 B（UVB）辐射]，导致 B 环打开，生成前维生素 D，也称为甾体。一旦形成，前维生素 D 可以通过热诱导异构化形成维生素 D，也可以吸收 UVB 辐射转化为包括胆钙化醇和麦角钙化醇在内的光产物。维生素 D 以及前维生素 D 光产物胆钙化醇和麦角钙化醇，都被细胞色素 P450（CYP）酶羟化为具有生物活性的羟基衍生物。其中最著名的是 1,25-二羟基维生素 D（1,25(OH)D），其在脊椎动物中的主要功能是调节钙和磷代谢。在此，我们综述了褪黑素的产生和代谢及其在昆虫中的功能的相关数据。我们讨论了真菌、植物和昆虫中前维生素 D 和维生素 D 及其光产物的产生，以及它们的酶激活机制，并提出了它们在这些生物群中的可能生物学功能。为了检测这些甾体和它们的前体和光产物以及褪黑素的代谢物，我们重点关注蜜蜂产生的蜂蜜和黑腹果蝇的身体提取物。我们讨论了褪黑素衍生物和甾体在昆虫中具有的共同生物学功能，如细胞保护和光保护作用。基于 ∆5,7 甾体和吲哚环的已知光生物学，我们提出了其他甾体和褪黑素犬尿酸代谢物的光产生的假设。我们还提供了这些独特分子的可能作用机制，并总结了不同生物（包括昆虫）中褪黑素能和甾体生成途径的差异和相似性。
