Vitamin B2: Riboflavin - Chemical Name, Structure, and Functions

1. Vitamin B2: Riboflavin Karilyne Manahan & Alyssa Specht

2. Chemical Name and Structure • Riboflavin also known as vitamin B2 and is an essential water-soluble vitamin • Chemical name: 7,8-dimethyl-10-ribityl-isoalloxazine1 • Chemical formula: C17H20N4O62 • Composed from 3 ring structure call flavin and 5 carbon chain sugar alcohol named ribitol2 • Gets name ribo-flavin

3. Major Coenzymes2 • Two coenzymes derived from B2 • Flavin mononucleotide (FMN) • Flavin adenine dinucleotide (FAD) • Formed by enzymes and composed of riboflavin and phosphate group (FMN) • FAD further adds additional adenosine phosphate group (AMP)

4. (2)

5. Chief Functions2 • Coenzymes FMN and FAD involved in several intermediary reactions involving flavoproteins • Flavoproteins - enzymes requiring FMN or FAD as coenzymes • Specifically in oxidation-reduction (redox) reactions

6. Redox Reactions2 • Essential for energy production by catabolizing carbohydrates, fats, and lipids to generate ATP by transferring electrons • Flavins act as oxidizing agents by accepting 2 hydrogen atoms and losing 2 elections • FMN and FAD reduced to FMNH2 and FADH2

7. Reducing of FMN or FAD2

8. FAD Reactions - Energy Production2 • Metabolic pathways involved in: • Pyruvate Dehydrogenase Complex • Fatty Acid Beta-Oxidation • acyl-CoA dehydrogenase • Citric Acid Cycle • α-ketoglutarate dehydrogenase and succinate dehydrogenase enzyme pathways • Complex II of Electron Transport Chain (ETC) • FADH2 converted to ATP in ETC (1.5 ATP)

9. FAD Reactions - Coenzyme Synthesis • B3 from tryptophan2 • Kyrureninase monooxygenase • Antioxidants3 • Xanthine oxidase to produce uric acid • Glutathione reductase to produce glutathione • Converts folate to active form2

10. Continue • aldehydes → carboxylic acids (aldehyde oxidase)2 • B6 → pyriodoxic acid • Retinol → retinoic acid

11. FMN Reactions2 • Energy production reactions • Complex I rxns in ETC • Synthesis reactions • Formation of coenzyme form of B6 (pyridoxal phosphate or PLP) • pyridoxine phosphate oxidase

12. Chief Functions: Disease Prevention and Treatment • Protective against diseases with root cause from oxidative stress and inflammation • Cardioprotection4 • Neuroprotection • Stoke5 and Migraine Treatment(6,7) • Cancer Inhibition(1,2,8) • metabolize carcinogens

13. Metabolic Pathways

14. Bioavailability • Riboflavin is not created or stored in the body9 must be consumed through diet • Mostly found as FAD form in foods; lesser amount FMN1 and little “free” riboflavin in foods10 • Must be converted to free riboflavin for absorption if bonded to proteins or if in FAD or FMN form2 • If bond to histidine or cysteine cannot be converted2

15. Digestion2 • Starts in stomach • Riboflavin-protein compounds → free riboflavin by hydrochloric acid • Then small intestine • FAD → FMN → free riboflavin at brush border (intestinal phosphatases)

16. Absorption • Once in free form can be absorbed2 • Major absorption site - proximal small intestine2 • Occurs through carrier mediated1 sodium-independent active transport2 • Per meal ~95% of riboflavin is absorbed2 • Max ~25mg

17. Metabolism & Transport2 • Quickly upon absorption into intestinal cell riboflavin → FMN (enzyme flavokinase) • **Requires ATP** • At serosal membrane • FMN → riboflavin - - > portal vein - - > liver - - > tissues

18. Metabolism & Transport2 • Flavins in blood mostly found as riboflavin (50%) with some FAD (40%) and FMN (10%) • FAD and FMN transported with protein carriers • albumin (primarily), fibrinogen, and globulins • Once transported to tissue absorbed by a carrier-mediated riboflavin-binding protein • High concentration enter by diffusion

19. Metabolism & Transport10 • In tissues: riboflavin → FMN • same process as earlier • Further FMN → FAD (enzyme FAD synthetase) • **Requires ATP** • Phosphatases in tissue can convert back flavins back to riboflavin

20. (2)

21. Excretion • Excreted through urine2 • Small amounts stored in • liver, spleen, sm intestine,kidneys, and heart2 • Can meet body’s needs for 2-6 weeks2 • Protects against toxicity9

22. Daily Recommended Intake • Glutathione reductase an adequate indicator of riboflavin requirements as its processes2 • reduction of glutathione disulfide --> glutathione is dependent upon FAD and NADPH • Meeting the DRI is not a large issue in the United States due to it’s fortification of many grains and cereals(11,12)

23. Daily Recommended Intake(1,2)

24. Deficiency • Ariboflavinosis (riboflavin disease in isolation) is rare • often in congruence with other vit./min. deficiencies(1,2) • Clinical Signs: • cheilosis, angular stomatitis, oral hyperemia, edema, seborrheic dermatitis, and neuropathy2 • Protein and DNA damage also possible due to GI phase of Cell cycle inhibited2 • Anemia, growth retardation, susceptibility to some carcinogens also possible2

25. Deficiency • Also related to B12 and folate deficiencies • Decreased riboflavin = ↓folate = ↓methionine → homocysteine (may ↑ CVD risk)1 • B12 derivative dependent on flavoproteins • Current treatment for riboflavin deficiency is 10-20 mg/d supplementation until symptoms are resolved1 • Other diseases that inc. risk of deficiency: • thyroid disease, DBM, chronic stress, depression, gastrointestinal diseases, cataracts(1,2)

26. Deficiency • Populations at Risk • Pregnant/lactating women, infants, school-aged children, elderly, athletes, vegetarians/vegans, alcoholics, anorexics, third world country populations1 • Lactating women have estimated 40-90% increased needs12 • Infants treated for hyperbilirubinemia at risk due to phototherapy treatment1

27. Toxicity • The body is protected from riboflavin toxicity due to its ability to readily excrete excess levels in the urine • No tolerable upper level intake has been established1

28. Significant Sources • Predominantly found as FAD in foods • Milk and eggs have high amounts of free riboflavin2 • these and other dairy products are primary sources of riboflavin13 • riboflavin in cow’s milk is 90% free form13 • Grains provide up to 20% daily requirements as whole grains or fortified products14 • Meat, legumes, and dark leafy vegetables are good sources2

29. Negative Effects on Riboflavin Content • Light has the biggest effect on riboflavin - up to 50% of riboflavin destroyed if held in light for only 2 hours3 • Oxidation15 • Trolox & ascorbic acid can reduce by antioxidant mechanisms • Fairly heat resistant, however pasteurization and UHT slightly lower levels13

30. Fortification & Additives • These processes enrich riboflavin content in foods making them good sources • Cost-effective way to increase riboflavin in foods → increase population intakes • Fortification is highly used in grain products • Additives, like improved lactic acid bacteria (LAB) strains added to yogurt to increase riboflavin synthesis16

31. References • Powers H. Riboflavin (vitamin B2) and health. AM J Clin Nutr. 2003; 77:1352-60. • Gropper S, Smith J. Advanced Nutrition and Human Metabolism. 6th ed. Belmont, CA: Wadsworth CENGAGE Learning; 2013. • Higdon J, Delage B, McNulty H, McCann A. Riboflavin. [Internet]. Oregon: Linus Pauling Institute. 2002 [2013]. Availible from:http://lpi.oregonstate.edu/infocenter/vitamins/riboflavin/ • Wang G, Li W, Zhao X. Riboflavin alleviates cardiac failure in type I diabetic cardiomyopathy. Heart Int [Internet]. 2011; 6(21): 75-79. • Zhou Y, Zhang X, Su F, Liu X. Importance of riboflavin kinase in the pathogenesis of stroke. CNS Neurosci Ther[Internet]. 2012 Oct 18(10):834-840. Available from Wiley Online Library: http://onlinelibrary.wiley.com/doi/10.1111/j.1755-5949.2012.00379.x/full • MacLennan SC, Wade FM, Forrest KM, Ratanayake PD, Fagan E, Antony J. High-dose riboflavin for migraine prophylaxis in children: a double-blind, randomized, placebo-controlled trial. J Child Neurol2008;23(11):1300-4. • Bruijn J, Duivenvoorden H, Passchier J, Locher H, Dijkstra N, Arts WF. Medium-dose riboflavin as a prophylactic agent in children with migraine: a preliminary placebo-controlled, randomised, double-blind, cross-over trial. Cephalalgia [Internet]. Mar 26 2010;30(12):1426-34. • Sharp L, Carsin A, Cantwell M, Anderson L, Murray L. Intakes of dietary folate and other B vitamins are associated with risks of esophageal adenocarcinoma, barrett’s esophagus, and reflux esophagitis. J Nutr[Internet]. 2013 Dec [cited March 20, 2014] 143(12):1966-1973. Available from: http://nutrition.highwire.org/content/143/12/1966.short • Subramanian V, Subramanya S, Ghosal A, Said H. Chronic alcohol feeding inhibits physiological and molecular parameters of intestinal and renal riboflavin transport. American Journal Of Physiology: Cell Physiology [Internet]. 2013, Sep, [cited March 20, 2014];305(5):C539-C546. Available from: Academic Search Complete.

32. References • Dey M, Mukherjee D, Dutta M, Mallik S, Ghosh D, Bandyopadhyay D. Flavin mono nucleotide phosphatase from goat heart: A forgotten enzyme of an important metabolic pathway. Journal Of Cell & Tissue Research [Internet]. 2013, Dec [cited March 20, 2014]; 13(3): 3851-3858. Available from: Academic Search Complete. • Feili Lo Y, Pei-Chun L, Yung-Ying C, Jui-Line W, Ning-Sing S. Prevalence of thiamin and riboflavin deficiency among the elderly in Taiwan. Asia Pacific Journal Of Clinical Nutrition [serial on the Internet]. 2005, Sept [cited March 20, 2014];14(3):238-243. Available from: Academic Search Complete. • Papathakis P, Pearson K. Food fortification improves the intake of all fortified nutrients, but fails to meet the estimated dietary requirements for vitamins A and B6, riboflavin and zinc, in lactating South African women. Public Health Nutrition [serial on the Internet]. 2012, Oct [cited March 20, 2014];15(10):1810-1817. Available from: Academic Search Complete. • Sunaric S, Denic M, Kocic G. Evaluation of riboflavin content in dairy products and non-dairy substitutes. Italian Journal Of Food Science [serial on the Internet]. (2012, Oct), [cited March 20, 2014]; 24(4): 352-357. Available from: Academic Search Complete. • Martinez-Villaluenga C, Michalska A, Frias J, Piskula M, Vidal-Valverde C, Zieliński H. Effect of Flour extraction rate and baking on thiamine and riboflavin content and antioxidant capacity of traditional rye bread. Journal Of Food Science [Internet]. (2009, Jan), [cited March 20, 2014];74(1):C49-C55. Available from: Academic Search Complete • Hall N, Chapman T, Kim H, Min D. Antioxidant mechanisms of Trolox and ascorbic acid on the oxidation of riboflavin in milk under light. Food Chemistry [Internet]. (2010, Feb), [cited March 20, 2014];118(3):534-539. Available from: Academic Search Complete. • Jayashree S, Rajendhran J, Jayaraman K, Kalaichelvan G, Gunasekaran P. Improvement of Riboflavin Production by Lactobacillus fermentum Isolated from Yogurt. Food Biotechnology [Internet]. 2011, July, [cited March 20, 2014]; 25(3): 240-251. Available from: Academic Search Complete.