Biological chemistry department

THE ROLE OF VITAMINS IN THE METABOLIC PROCESSES OF HUMANS

© Assoc Prof O.S. Shkoda, 2017 • Polish biochemist Casimir Funk discovered vitamin B1 in 1912 in rice bran.

• He proposed the complex be named "Vitamine" (vital amines).

• By the time it was shown that not all vitamins were amines, the word was already ubiquitous.

2 Vitamins (from lat. vita and aminum – meaning amine of life) – bioorganic compound and a vital nutrient, which are: 1. Essential components of cellular and extracellular Metabolones

2. Not synthesized in the body, where it comes totally with food (are nutrients)

3.Necessary for the organism in small amounts (10-3 – 10-6 grams per day) 3 A VITAMER of a particular vitamin is any of a number of chemical compounds, generally having a similar molecular structure, each of which shows vitamin-activity in a vitamin- deficient biological system.

(Vitamin A has at least six vitamer chemicals that all qualify as "vitamin A", each with slightly different properties)

4 A PROVITAMIN is a substance that may be converted within the body to a vitamin. (They do not form coenzyme forms)

β-carotene – provitamin А, nicotine – provitamin B3, ergosterol, 7-dehydrocholesterol – provitamins D

5 Antivitamins – are substances of the different chemical nature, which restricts the use of vitamins in the body and lead to pseudo-vitamin failure:

• Are structural analogues of vitamin and operate on the principle of competitive interaction with enzymes (Methotrexate,

Sulfanilamides – antivitamins Вс; Isoniazid, Phthivazidum – antivitamins В6)

• Modify the chemical structure of vitamins, inhibit their absorption, transport, cell absorption, which lead to the manifestation of hypovitaminosis (ethyl alcohol, Barbiturates, Phenytoin) 6 Classification of Vitamins

By solubility in water and lipids (fats):

 Water-soluble (hydrophilic) В1, В2, В3 (PP), В5, В6, B7 (H), B9, B12, С

 Fat-soluble (lipophilic) А, D, E, K

7 WATER-SOLUBLE VITAMINS

 Have a weak ability to accumulation, which limits the body's resistance in the conditions of hypovitaminosis

 Cells consume water-soluble vitamins by the principle of quantum satis, the rest is excreted unchanged by the kidneys, partially metabolized in the liver and excreted in the bile

8 FAT-SOLUBLE VITAMINS

1.Absorbed in the intestine exclusively in combination with lipids 2. Transported usually by chylomicrons and plasma albumins 3.May be deposited by lipocytes of the liver (Ito cells) 4.Accumulated in adipose tissue (at hypervitaminosis)

9 Classification of vitamins

On the pharmacodynamic characteristics (the main molecular mechanism of action):

 Coenzymes - water-soluble vitamins are used for the synthesis of coenzymes included in the major key enzymes of metabolic pathways

 Redox vitamins - natural antioxidants that inactivate Reactive oxygen species and lipid peroxides, protecting biological membrane and cellular structures from toxic peroxidation products (oxidative stress)

 Hormone-vitamins - vitamins, after which certain structural modifications can penetrate karyoplasm with influence on gene expression

10 Classification of vitamins According to their biological action (take into account the pathology that occurs when concretized hypovitaminosis) Empirical name and chemical structure The main biological effect

В1 (thiamine), В2 (riboflavin), В5 (pantothenic acid), Dermatitis В6 (pyridoxine)

В12 (cyanocobolamin), В9 (folates) Anemia С (ascorbic acid) Scurvy РР or B3 (niacin) Pellagra Р (flavonoids) reduce oxidative stress and related signaling pathways in blood vessel cells 11 Classification of vitamins 2. According to their biological action (take into account the pathology that occurs when concretized hypovitaminosis)

Empirical name and chemical The main biological structure effect А (retinol) Xerophthalmia, Growth Vitamin К (phylloquinone) Bleeding diathesis Е (α-tocopherol) Sterility in males D (cholecalciferol) Rickets

12 Vit А (retinol) Daily intake – 1,0 mg (CH=CH-C=CH)2-CH2OH CH3 Liver, orange, ripe yellow Isoprenoid tail fruits, leafy vegetables, Vit А1 β-ionon carrots, spinach, fish, milk

Active forms 1. Retinal – vision act. When the 11-cis-retinal chromophore absorbs a photon it isomerizes from the 11-cis state to the all-trans state 2. Retinoic acid (tretinoin)  Taking part in embryonic development  high teratogenicity  used for treatment of cancer and acne

Retinoic acid acts by binding to the retinoic acid receptor (RAR), which is bound to DNA as a heterodimer with the retinoid X receptor (RXR) in regions called retinoic acid response elements (RAREs).

13 Vitamin A and vision

 Vit. A is necessary to form rhodopsin (in rodes, night vision) and iodopsins (photopsins, in cones – color vision) - visual PIGMENT.  Retinaldehyde is a prosthetic group of light- sensitive opsin protein.  In the retina, all-trans-retinol is isomerized to 11- cis-retinol → oxidized to 11-cis-retinaldehyde, this reacts with opsin (Lys) → to form the holoprotein rhodopsin.  Absorption of light → conformation changes of opsin → photorhodopsin. The RARs and their action. RA is transported to the nucleus by the protein cellular RA–binding protein (CRABP) and delivered to the RARα. RARα heterodimerizes with and binds to RARE present most often in gene promoters. In the classical pathway of RA action, RA binds to dimers of RARα and RXRs (α, β, or γ) to induce expression of its downstream target genes, including RARβ. Upon activation, RARβ can regulate its own expression and that of its downstream genes, the function of which is mainly to inhibit cell growth. Contrary to the differentiation functions attributed to the classical pathway, the nongenomic pathways exert strong antiapoptotic and proliferative effects on cancer cells. It is believed that the classical and nongenomic pathways are controlled by the relative abundance of their own ligands. RA has a stronger affinity for RARs than for the other receptors, and the classical pathway plays a dominant role over the nongenomic pathways. Thus, if RA is present with other ligands such as estrogen, signaling through the classical pathway is preferred to result in cell differentiation and growth inhibition. Vit Е (tocopherols) Daily intake – 10-20 mg CH3 HO Many fruits and CH3 vegetables, nuts (CH2-CH2-CH-CH2)3-H and seeds H3C O Olive Oil CH3 CH3 Active part

Main effects: Antiradicalic (scavenger of free radicals)

antiperoxidant (lipid peroxidant chain)

membranoprotector 16 Coupled redox reaction of vitamin E and vitamin C (co-antioxidants) during the reduction (scavenging) of peroxyl radicals (A) and proposed scheme of the mechanisms that may lead vitamin E copolymers to control the flux of reactive oxygen species in the extracorporeal circulation (B). ROS: Reactive oxygen species; Vit C: Ascorbic acid; Vit C-: Ascorbate anion; Vit C-*: Ascorbyl radical - - + anion; DHA: Dehydroascorbate; O2: Molecular oxygen; O2 *: Superoxide anion; e /H : Electron/proton; T-OH: Tocopherol; T-O*: Tocopheryl radical; ROOH: Peroxyde (reduced form); ROO*: Peroxyl radical.

Galli F. Vitamin E-derived copolymers continue the challenge to hemodialysis biomaterials. World J Nephrol 2012; 1(4): 100-105 Md Saidur Rahman, Woo-Sung Kwon, and Myung-Geol Pang, “Calcium Influx and Male Fertility in the Context of the Sperm Proteome: An Update,” BioMed Research International, vol. 2014, Article ID 841615, 13 pages, 2014. doi:10.1155/2014/841615 Vit D (cholecalciferol – D3, ergocalciferol – D2) Fish, eggs, liver, mushrooms Daily intake – 10 g

Calcitriol biosyntesis; 1. Forming cholecalciferol from 7-dehydrocholecterol in skin by UVB 2. Transport to liver 3. 25-hydroxylation 4. Transport to kidney 5. 1-hydroxylation – forming hormone cacitriol 19 Vitamin D binds to a “vitamin D binding protein” (VDP) for transport to target organs.

Vitamin D is not active itself (it’s a prohormone); it is modified to yield biologically active forms, such as calcitriol.

Calcitriol (derived from vitamin D) is a transcription factor, influencing expression of proteins involved in calcium absorption and transport.

Vitamin D is also important for immune system function.

Deficiency causes rickets, bone loss. O Vit К (phylloquinone) Dailly intake – 120 g CH3

CH3 CH3

CH2 CH C CH2 (CH2-CH2-CH-CH2)3H O Isoprenoid tail naphtoquinone Leafy green vegetables Mechanism of action:  involved in the carboxylation of certain glutamate residues in proteins to form gamma-carboxyglutamate (Gla) residues

Biological effects:  Blood coagulation: prothrombin (factor II), factors VII, IX, and X, and proteins C, S, and Z  Bone metabolism  Vascular biology: growth arrest-specific protein 6

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NH2 Vit В (Thiamine) CH3 1 N N Daily intake– 1,2 mg 5 H C N 2 S CH -CH -OH 3 2 2 Pork, oatmeal, brown rice, vegetables, potatoes, liver, eggs 2-active center The transformation to the co-enzyme form:

thiamine diphosphokinase thiamine+ АТP thiamine diphosphate (ТPP) + АМP TPP works as a coenzyme in many enzymatic reactions, such as: • Pyruvate dehydrogenase complex • Pyruvate decarboxylase in ethanol fermentation • Alpha-ketoglutarate dehydrogenase complex • Branched-chain amino acid dehydrogenase complex • 2-hydroxyphytanoyl-CoA lyase • Transketolase 24 Vitamin B1 - deficiency

1. Mild deficiency – leads to gastrointestinal complients, weakness 2. Moderate deficiency - peripheral neuropathy, mental abnormalities, ataxia 3. Full-blown deficiency - beri-beri – characterized with severe muscle weakness, muscle wasting and delirium, paresis of the eye muscles, memory loss. Degeneration of the cardiovascular system. Beri-beri causes long-term consumption of foods rich in carbohydrates but poor in thiamine - husked rice, white flour and refined sugar.

25 10 O

H3C N Vit В2 (riboflavin) NH Daily intake – 1.3 mg

H C N N O 3 1 Dairy products, bananas, H H 1, 10 –active center popcorn, green beans, H OH asparagus H OH riboflavin kinaze H OH Riboflavin + АТP FMN + АDP CH2-OH FAD Synthaze FMN + ATP FAD + Н4Р2О7

FMN – Complex I and II Electron transport chain. FAD – succinate dehydrogenase, Acetyl-CoA-dehydrogenases (beta- oxidation of fatty acids), glycerol-3-phosphate dehydrogenase (triglyceride synthesis) and xanthine oxidase involved in purine nucleotide catabolism

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Causes of vitamin B2 deficiency • Lack of dietary vitamin B.

• A result of conditions that affect absorption in the intestine.

• The body not being able to use the vitamin.

• An increase in the excretion of the vitamin from the body.

Vitamin B2 – symptoms of deficiency • Cracked and red lips. • Inflammation of the lining of mouth and tongue. • Dry and scaling skin- keratitis, dermatitis and iron-deficiency anemia 29 4 – active center Vit B , РР (Niacin), O 3 4 Dailly intake – 13-19 mg COOH C NH -NH3 2 Meat, fish, +NH eggs, many N 3 N vegetables, Nicotinic acid nicotinamide mushrooms, The transformation to the co-enzyme form: tree nuts

nicotinamide adenine dinucleotide (NAD) is involved in redox reactions, carrying electrons from one reaction to another.

NADP is a cofactor used in anabolic reactions, such as lipid and nucleic acid synthesis, which require NADPH as a 30 reducing agent

Niacin is not a true vitamin in the strictest definition since, as indicated above, the NAD+ can be derived from the amino acid tryptophan. However, the ability to utilize tryptophan for niacin synthesis is inefficient (60 mg of tryptophan are required to synthesize 1 mg of niacin). Also, synthesis of niacin from tryptophan

requires vitamins B1, B2 and B6 which would be limiting in themselves on a marginal diet.

Vitamin B3 - deficiency • Pellagra: A serious deficiency of niacin. • The main results of pellagra can easily be remembered as "the four D's": diarrhea, dermatitis, dementia, and death. • Pelagra is very rare now, except in alcoholics, strict vegetarians, and people in areas of the world with very poor nutrition.

• Milder deficiencies of niacin can cause dermatitis around the mouth and rashes, fatigue, irritability, poor appetite, indigestion, diarrhea, headache. Vit В5 (Pantothenic acid), CH3 OH Daily intake – 5 mg HO CH2 C CH C N CH2 CH2 COOH H Meat, broccoli, avocados CH3 O

Animals require pantothenic acid to synthesize coenzyme-A (CoA)

Since coenzyme A is, in chemical terms, a thiol, it can react with carboxylic acids to form thioesters, thus functioning as an acyl group carrier. It assists in transferring fatty acids from the cytoplasm to mitochondria. A molecule of coenzyme A carrying an acetyl group is also referred to as acetyl-CoA. When it is not attached to an acyl group, it is usually referred to as 'CoASH' or 'HSCoA’

Deficiency of pantothenic acid is extremely rare due to its widespread distribution in whole grain cereals, legumes and meat. Symptoms specific to pantothenate deficiency are difficult to assess since they are subtle and resemble those of other B vitamin deficiencies. These symptoms include painful and burning feet, skin abnormalities, retarded growth, dizzy spells, digestive disturbances, vomiting, restlessness, stomach stress, and muscle cramps. 34 Meat, vegetables, tree nuts, bananas Vit В6 (Pyridoxine) Daily intake – 1.3-1.7 mg

CH2NH2 CH2OH O CH

HO CH2OH HO CH2OH HO CH2OH -NH3 -2H

+NH3 +2H H3C N H3C N H3C N pyridoxamine pyridoxine pyridoxal 4-active center Cofactor – Pyridoxal 5'-phosphate (PLP):  in all transamination reactions, and in certain decarboxylation, deamination, and racemization reactions of amino acids  serine dehydratase (gluconeogenesis)

35 The aminotransferase mechanism

36 Deficiencies of vitamin B6 are rare and usually are related to an overall deficiency of all the B-complex vitamins. Like the role of chronic alcohol consumption and an associated poor diet leading to thiamine deficiency, alcoholism is the leading cause of deficiency in

B6.

Symptoms that may appear with deficiency in vitamin B6 include nervousness, insomnia, skin eruptions, loss of muscular control, anemia, mouth disorders, muscular weakness, dermatitis, arm and leg cramps, loss of hair, slow learning, and water retention.

37 Vit B9 or ВС (folic acid) Daily intake – 400 г

Leafy vegetables, pasta, bread, cereal, liver

38 Folate must be converted to the active coenzyme, tetrahydrofolate, by two successive redox reactions catalyzed by dihydrofolate reductase

THF is a cofactor in many reactions, especially in the metabolism of amino acids and nucleic acids. It acts as a donor of a group with one carbon atom

Folic acid deficiency results in elevated levels of homocystein.

Deficiency in pregnant women can lead to birth defects 39 Vit В12 (cobalamin) Extrinsic factor Daily intake – 2,4 g

In the body it is converted to the human physiological forms methylcobalamin and 5'-deoxyadenosylcobalamin Note that the corrin ring of vitamin B12 is similar, but not identical, to the porphyrin ring found in heme-containing proteins. Vitamin B12 is not used as a source of heme 40 In humans, vitamin B12 has only two known functions: 1) in the methionine synthase reaction, vitamin B12 accepts a methyl group from methyl-THF and donate it to homocysteine to form methionine and 2) vitamin B12 is a coenzyme for methylmalonyl-CoA mutase, which catalyzes the rearrangement of methylmalonyl- CoA (from odd chain fatty acid metabolism and some amino acids) to succinyl-CoA. Vitamin B12 is not made in plants; it is only synthesized by microorganisms Deficiency in vitamin B12 results in a potentially lethal condition called pernicious anemia 41 Vit Н, В7 (Biotin) Daily Intake – 30 g Egg , liver, peanuts, leafy green vegetables

Animals have four biotin dependent enzyme complexes: 1) Pyruvate carboxylase, the first step in of the gluconeogenic pathway from pyruvate, and an important source of oxaloacetate for the TCA cycle. 2) Acetyl-CoA carboxylase, the control step for fatty acid synthesis (this enzyme converts acetyl-CoA to malonyl-CoA). 3) Propionyl-CoA carboxylase, which produces methylmalonyl-CoA, the first step in the conversion of propionyl CoA (generated from odd-chain fatty acid and some amino acid oxidation) to succinyl-CoA, which can enter the TCA cycle. 4) β-Methylcrotonyl-CoA carboxylase, an enzyme required for oxidation of leucine and some isoprene derivatives.

42 The reactions catalyzed by the pyruvate dehydrogenase complex are: 1. Addition of the ketoacid (pyruvate) to thiamin pyrophosphate at the position next to the N+ (carbanion addition) to form a hydroxyethyl product, with release of the carboxylate as CO2. 2. Reaction of lipoamide with the hydroxy ethyl product to re-form free thiamin pyrophosphate and acetyl lipoamide. 3. Reaction of acetyl lipoamide with CoA-SH to form acetyl-CoA and dihydrolipoamide. 4. Reduction of FAD by the dihydrolipoamide. 5. Reduction of NAD+ by the FADH2 to NADH 43 Vit С (ascorbic acid) Daily intake– 90 mg

Many fruits and vegetables, liver

1. a cofactor in at least eight enzymatic reactions, including several collagen synthesis reactions that, when dysfunctional, cause the most severe symptoms of scurvy. prolyl-3-hydroxylase, prolyl-4-hydroxylase, and lysyl hydroxylase are required for the hydroxylation of proline and lysine in the synthesis of collagen. ε-N-trimethyl-L-lysine hydroxylase and γ-butyrobetaine hydroxylase that are necessary for synthesis of carnitine dopamine beta hydroxylase participates in the biosynthesis of norepinephrine from dopamine. Peptidylglycine alpha-amidating monooxygenase amidates peptide hormones by removing the glyoxylate residue from their c-terminal glycine residues. This increases peptide hormone stability and activity. 4-hydroxyphenylpyruvate dioxygenase modulates tyrosine metabolism 44 2. Antioxidant properties Reduction ions Fe3+, acceptation of ROS

3. Absorption of iron in GIT

4. Immune system. it has been hypothesized to modulate the activities of phagocytes, the production of cytokines and lymphocytes, and the number of cell adhesion molecules in monocytes

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