Riboflavin (B2)

Front 1

Riboflavin (B2)

Back 1

“Flavus” – Latin for yellow “Ribo” – Presence of ribose-like side chain 3 linked 6 member rings with sugar alcohol attached to middle ring 2 Coenzymes FMN – Flavin Mononucleotide FAD – Flavin Adenine Dinucleotide

Front 2

Sources of Riboflavin

Back 2

Greatest source (1/4) from milk and milk products Then bread products and fortified cerealsBest sources – Enriched flour products, eggs, meatGood Sources – Liver, mushrooms, spinach, green leafy veg, broccoli, asparagus, milk, cottage cheese

Front 3

Sources of Riboflavin

Back 3

Exposure to Light – UV radiation causes riboflavin to breakdown rapidly Products should be packaged in paper and plastic containers vs glass to prevent breakdown Especially milk (products) and cereals

Front 4

Digestion of Riboflavin

Back 4

Digestion of RiboflavinForm in food variesFree or protein-bound in milk, eggs and enriched foods Other foods as coenzyme FMN/FADHCl in stomach – Frees riboflavin bound to proPhosphatase enzymes – Frees phosphate prior to absorption

Front 5

Absorption of Riboflavin

Back 5

Bioavailability - ~95% abs, up to max of ~27 mg/mealAbs proportionate to intakeIncreased abs with presence of other foods and bile salts Animal sources thought to be better abs than plantsFree riboflavin abs mainly through active transport Passive diffusion with large amount of intake

Front 6

Absorption of Riboflavin

Back 6

Inhibition of AbsorptionDivalent Metals – Chelates riboflavincopper, zinc, iron, manganeseETOH – Impairs digestion and absorption

Front 7

Absorption of Riboflavin

Back 7

Sent to liver – Converted to FMN and then to FAD FAD is predominant flavoenzyme in tissue Most tissues can convert to coenzyme form but mainly done in small intestine, liver, heart and kidneys

Front 8

Transport of RiboflavinIn plasma

Back 8

– Mainly as free riboflavinAlso bound to proteins – Mainly albumin but also fibrinogen and globulinsCells – can convert to coenzymes

Front 9

Storage of Riboflavin

Back 9

Storage of Riboflavin Small amount in liver, kidney and heart

Front 10

Excretion of Riboflavin

Back 10

Excess intake excreted primarily in urine Urine may be florescent yellowSmall amount in feces – Some may be from catabolism of riboflavin by intestinal flora

Front 11

Functions of Riboflavin

Back 11

Coenzyme – FMN and FAD take part in redox reactionsCritical role in metabolism of CHO, lipid and pro and electron transport chainAlso with Cytochrome P450 in metabolism of drugs/toxins

Front 12

Functions of Riboflavin

Back 12

Oxidation-reduction reactions Electrons are transferred in a series of reactions from energy-yielding compounds eventually to oxygen Form water and release energy (ATP) Oxidation – Loss of electron (or gains oxygen or loses H+) Reduction – Gain of electron (or loses oxygen or gains H+) FAD – Oxidized form of coenzyme When reduced gains 2 electrons (H+) ->FADH2

Front 13

Functions of Riboflavin

Back 13

Energy Metabolism Citric Acid Cycle – Oxidation of succinate->fumarate Requires FAD containing enzyme succinate dehydrogenase FADH2 is formed ->donates H+ to electron transport chain FA Breakdown (beta-oxidation) FA -> Acetyl CoA Fatty acid dehydrogenase requires FAD

Front 14

Functions of Riboflavin

Back 14

Energy Metabolism

Electron transport chain

– FMN and FAD involved in transferring electronsPyruvate->Acetyl CoAFAD involved in reaction

Front 15

Functions of Riboflavin

Back 15

Activation of Other B Vitamins Formation of Niacin Tryptophan -> Niacin requires FAD Formation of Active vit B6 coenzyme Pyridoxal phosphate-requires FMN Synthesis of folate metabolite 5-methyl-tetrahydrofolate (active folate) Riboflavin indirectly participates in homocysteine metabolism

Front 16

Functions of Riboflavin -

Back 16

Antioxidant Synthesis of GlutathioneGlutathione reductase – FAD dependent enzymeProtects from ROS

Catabolism of purine in liverAldehyde Oxidase – Enzyme for aldehydes ex. Retinal -> Retinoic acidNeurotransmitter metabolismSynthesis of deoxyribonucleotides (DNA)Assist with structure/folding of certain proteins

Front 17

Riboflavin Deficiency - Ariboflavinosis

Back 17

Generally, not only deficient in riboflavin in isolation Often with other nutrient deficiencies Can develop def in 2 months, can see s/s within 4 months Severe deficiency can lead to protein and DNA damage

At Risk – Elderly, Adolescent females, cancer, CVD, DM, Alcoholism, malabsorption d/o, poor diet, developing countries, trauma/stress (increased excretion) Phenobarbital – seizure med Long term use can lead to def Drug increases breakdown of riboflavin and other nutrients in liver

Front 18

Riboflavin Deficiency - Ariboflavinosis

Back 18

Some s/s may be 2/2 other B-vit def as they work in same metabolic pathways and often supplied by same foods Since involved with metabolism of other B vit,def in riboflavin may affect other enzyme systems S/S – Inflammation of throat, stomatitis, glossitis, angular cheilitis, seborrheic dermatitis Anemia, fatigue, confusion, HA

Iron – Riboflavin def alters iron metabolism Research suggests may impair iron absorption, increaseintestinal loss and/or impair iron utilization forsynthesis of Hgb

Front 19

Riboflavin Toxicity

Back 19

No UL set - No adverse effects from consuming large amountLack of harm may be 2/2 limited solubility and limited capacity for absorption in GITPlus rapid excretion in urine

Front 20

Assessment of Riboflavin

Back 20

Measure erythrocyte glutathione reductase Uses FAD as coenzyme – Activity limited if def Measure erythrocyte Flavin - >90% as coenzyme Measure urinary excretion

Front 21

Riboflavin and Chronic Disease

Back 21

Riboflavin and Chronic Disease Cancer – Folate def and increased homocysteine may increase cancer risk Riboflavin intake is a determinant of homocysteine concentration Therefore – Riboflavin status can influence metabolism of folate thereby potentially affecting cancer risk One study – Inverse correlation with riboflavin intake and colorectal cancer risk

Cataracts – Observational studies

Some support for role of riboflavin in prevention of cataracts