Compendium of the most significant studies with reference to properties, intake, effects.

Suwannasom N, Kao I, Pruß A, Georgieva R, Bäumler H. Riboflavin: The Health Benefits of a Forgotten Natural Vitamin. Int J Mol Sci. 2020 Jan 31;21(3):950. doi: 10.3390/ijms21030950.

Abstract. Riboflavin (RF) is a water-soluble member of the B-vitamin family. Sufficient dietary and supplemental RF intake appears to have a protective effect on various medical conditions such as sepsis, ischemia etc., while it also contributes to the reduction in the risk of some forms of cancer in humans. These biological effects of RF have been widely studied for their anti-oxidant, anti-aging, anti-inflammatory, anti-nociceptive and anti-cancer properties. Moreover, the combination of RF and other compounds or drugs can have a wide variety of effects and protective properties, and diminish the toxic effect of drugs in several treatments. Research has been done in order to review the latest findings about the link between RF and different clinical aberrations. Since further studies have been published in this field, it is appropriate to consider a re-evaluation of the importance of RF in terms of its beneficial properties.

de Souza AC, Kodach L, Gadelha FR, Bos CL, Cavagis AD, Aoyama H, Peppelenbosch MP, Ferreira CV. A promising action of riboflavin as a mediator of leukaemia cell death. Apoptosis. 2006 Oct;11(10):1761-71. doi: 10.1007/s10495-006-9549-2. 

Abstract. Besides having a pivotal biological function as a component of coenzymes, riboflavin appears a promissing antitumoral agent, but the underlying molecular mechanism remains unclear. In this work, we demonstrate that irradiated riboflavin, when applied at microM concentrations, induces an orderly sequence of signaling events finally leading to leukemia cell death. The molecular mechanism involved is dependent on the activation of caspase 8 caused by overexpression of Fas and FasL and also on mitochondrial amplification mechanisms, involving the stimulation of ceramide production by sphingomyelinase and ceramide synthase. The activation of this cascade led to an inhibition of mitogen activated protein kinases: JNK, MEK and ERK and survival mediators (PKB and IAP1), upregulation of the proapoptotic Bcl2 member Bax and downregulation of cell cycle progression regulators. Importantly, induction of apoptosis by irradiated riboflavin was leukaemia cell specific, as normal human lymphocytes did not respond to the compound with cell death. Our data indicate that riboflavin selectively activates Fas cascade and also constitutes a death receptor-engaged drug without harmful side effects in normal cells, bolstering the case for using this compound as a novel avenue for combating cancerous disease.

Martínez-Limón A, Calloni G, Ernst R, Vabulas RM. Flavin dependency undermines proteome stability, lipid metabolism and cellular proliferation during vitamin B2 deficiency. Cell Death Dis. 2020 Sep 7;11(9):725. doi: 10.1038/s41419-020-02929-5. 

Abstract. Tumor cells adapt their metabolism to meet the energetic and anabolic requirements of high proliferation and invasiveness. The metabolic addiction has motivated the development of therapies directed at individual biochemical nodes. However, currently there are few possibilities to target multiple enzymes in tumors simultaneously. Flavin-containing enzymes, ca. 100 proteins in humans, execute key biotransformations in mammalian cells. To expose metabolic addiction, we inactivated a substantial fraction of the flavoproteome in melanoma cells by restricting the supply of the FMN and FAD precursor riboflavin, the vitamin B2. Vitamin B2 deficiency affected stability of many polypeptides and thus resembled the chaperone HSP90 inhibition, the paradigmatic multiple-target approach. In support of this analogy, flavin-depleted proteins increasingly associated with a number of proteostasis network components, as identified by the mass spectrometry analysis of the FAD-free NQO1 aggregates. Proteome-wide analysis of the riboflavin-starved cells revealed a profound inactivation of the mevalonate pathway of cholesterol synthesis, which underlines the manifold cellular vulnerability created by the flavoproteome inactivation. Cell cycle-arrested tumor cells became highly sensitive to alkylating chemotherapy. Our data suggest that the flavoproteome is well suited to design synthetic lethality protocols combining proteostasis manipulation and metabolic reprogramming.

Powers HJ, Corfe BM, Nakano E. Riboflavin in development and cell fate. Subcell Biochem. 2012;56:229-45. doi: 10.1007/978-94-007-2199-9_12. 

Abstract. Riboflavin (7,8-dimethyl-10-ribitylisoalloxazine; vitamin B2) is a water-soluble vitamin, cofactor derivatives of which (FAD, FMN) act as electron acceptors in the oxidative metabolism of carbohydrate, amino acids and fatty acids and which in the reduced state can donate electrons to complex II of the electron transport chain. This means that riboflavin is essential for energy generation in the aerobic cell, through oxidative phosphorylation. The classic effects of riboflavin deficiency on growth and development have generally been explained in terms of these functions. However, research also suggests that riboflavin may have specific functions associated with cell fate determination, which would have implications for growth and development. In particular, riboflavin depletion interferes with the normal progression of the cell cycle, probably through effects on the expression of regulatory genes, exerted at both the transcriptional and proteomic level.

Henriques BJ, Lucas TG, Gomes CM. Therapeutic Approaches Using Riboflavin in Mitochondrial Energy Metabolism Disorders. Curr Drug Targets. 2016;17(13):1527-34. doi: 10.2174/1389450117666160813180812. 

Abstract. Riboflavin, or vitamin B2, plays an important role in the cell as biological precursor of FAD and FMN, two important flavin cofactors which are essential for the structure and function of flavoproteins. Riboflavin has been used in therapeutic approaches of various inborn errors of metabolism, notably in metabolic disorders resulting either from defects in proteins involved in riboflavin metabolism and transport or from defects in flavoenzymes. The scope of this review is to provide an updated perspective of clinical cases in which riboflavin was used as a potential therapeutic agent in disorders affecting mitochondrial energy metabolism. In particular, we discuss available mechanistic insights on the role of riboflavin as a pharmacological chaperone for the recovery of misfolded metabolic flavoenzymes.

Bacher A, Eberhardt S, Fischer M, Kis K, Richter G. Biosynthesis of vitamin b2 (riboflavin). Annu Rev Nutr. 2000;20:153-67. doi: 10.1146/annurev.nutr.20.1.153. 

Abstract. The biosynthesis of one riboflavin molecule requires one molecule of GTP and two molecules of ribulose 5-phosphate as substrates. The imidazole ring of GTP is hydrolytically opened, yielding a 4, 5-diaminopyrimidine which is converted to 5-amino-6-ribitylamino-2, 4(1H,3H)-pyrimidinedione by a sequence of deamination, side chain reduction and dephosphorylation. Condensation of 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione with 3, 4-dihydroxy-2-butanone 4-phosphate obtained from ribulose 5-phosphate affords 6,7-dimethyl-8-ribityllumazine. Dismutation of the lumazine derivative yields riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione, which is recycled in the biosynthetic pathway. The structure of the biosynthetic enzyme, 6,7-dimethyl-8-ribityllumazine synthase, has been studied in considerable detail.

Kasai S, Nakano H, Kinoshita T, Miyake Y, Maeda K, Matsui K. Intestinal absorption of riboflavin, studied by an in situ circulation system using radioactive analogues. J Nutr Sci Vitaminol (Tokyo). 1988 Jun;34(3):265-80. doi: 10.3177/jnsv.34.265.

Abstract. The intestinal absorption of riboflavin was studied using radioactive riboflavin and its analogues 8-demethylriboflavin, 3-methylriboflavin, 5'-deoxyriboflavin, 2'-deoxyriboflavin, 7,8-dimethyl-10-hydroxyethylisoalloxazine, lumiflavin, lumichrome, and riboflavin-5'-monosulfate, which were synthesized with high specific radioactivity. A specific absorption of riboflavin at dietary concentrations was confirmed using an in situ circulation system. The relation between the chemical structure of flavins and the absorption mechanism was studied using this system. The 8-demethylriboflavin, an analogue modified at benzene moiety of the isoalloxazine ring, was absorbed in a similar way to riboflavin, by dual kinetics: by a process specific for riboflavin at dietary concentrations and by simple diffusion (nonspecific absorption) predominating at higher concentrations (over 100 microM). However, 3-methylriboflavin and analogues modified at the ribityl group, including 5'-deoxyriboflavin, were absorbed only via simple diffusion even at dietary concentrations. Many flavins examined, except for 3-isobutylriboflavin, 3-carboxymethylriboflavin, lumichrome, and riboflavin-5'-monosulfate, interfered with the specific absorption of riboflavin. It was concluded from these results that one of the specific absorption processes for riboflavin is a phosphorylation-dephosphorylation process. Four water-soluble vitamins did not interfere with the specific absorption of riboflavin, indicating that these vitamins do not share a common specific absorption pathway with riboflavin.

Larrea L, Calabuig M, Roldán V, Rivera J, Tsai HM, Vicente V, Roig R. The influence of riboflavin photochemistry on plasma coagulation factors. Transfus Apher Sci. 2009 Dec;41(3):199-204. doi: 10.1016/j.transci.2009.09.006. 

Abstract. Studies with riboflavin in the 1960s showed that it could be effective at inactivating pathogens when exposed to light. The principal mode of action is through electron transfer reactions, most importantly in nucleic acids. This suggested that it could act as a photosensitizer useful in the inactivation of pathogens found in blood products. Objective: To study the influence of photo-inactivation with riboflavin on the coagulation factors of plasma....Conclusions: As with other pathogen reduction procedures for plasma products, treatment with riboflavin and UV light resulted in reduction in the activity levels of several pro-coagulant factors. Coagulation inhibitors are well preserved.

Namazi N, Heshmati J, Tarighat-Esfanjani A. Supplementation with Riboflavin (Vitamin B2) for Migraine Prophylaxis in Adults and Children: A Review. Int J Vitam Nutr Res. 2015;85(1-2):79-87. doi: 10.1024/0300-9831/a000225.

Abstract. Background and aim: Migraine is a unilateral and pulsating headache associated with nausea, photophobia, vomiting, and sensitivity to light. Low vitamin B2 can lead to mitochondrial dysfunction and may have an effect on migraine pathogenesis. The aim of the present study was to carry out a review of existing evidence regarding the effects of riboflavin (vitamin B2) supplementation on migraine prophylaxis in adults and children....Conclusions: It seems that riboflavin is a safe and well-tolerated option for preventing migraine symptoms in adults, however, there is insufficient evidence to make recommendations regarding vitamin B2 as an adjunct therapy in adults and children with migraine.