Vitamin B1

Vitamin B1

generality

La Vitamin B1, Also known as Thiamin o aneurin, it's a micronutrient vitamin essential e water-soluble part of the group B.


It is found in many foods (plant and animal) but a concentrations limited. There is therefore the possibility of shortage nutritional (almost non-existent in the West), which in the most serious cases can lead to beri-beri; the relative neuropathic syndrome due to thealcoholism.


Vitamin B1, in all its active forms, has numerous metabolic functions; among these above all of coenzyme catalyst - for example in the way of carbohydrates and in that of amino acids.


Its needs are about 0,4 mg each 1000 kcal ingested. Well tolerated and rarely toxic, it can be supplemented or administered by injection; only in the latter case can it give side effects.

Let's go into detail.

For further information: Thiamine

Professional Chermisty

Introduction to the chemistry of vitamin B1

Vitamin B1 was discovery in 1897. It was the first vitamin element to be isolated (in 1926) and then synthesized (in 1936).


Vitamin B1 is a compound sulphurous organic colorless with chemical formula C12H17N4OS. Its structure is composed of an aminopyrimidine and a thiazole ring connected by a methylene bridge. Thiazole can be replaced by methyl and hydroxyethyl side chains.

Vitamin B1 is water soluble (water-soluble), methanol and glycerol, but practically insoluble in other organic solvents. Show stability a acidic pH, but it is unstable in alkaline solutions.

In vivo, being a persistent carbene, vitamin B1 comes metabolized at the enzymatic level to catalyze benzoin condensations.


Vitamin B1 turns out thermolabile in cooking, but stable al freezing. IS susceptible to the light ultraviolet and irradiation gamma e reacts strongly to reactions of Maillard.

Synthesis

Synthesis of vitamin B1

They can carry out the biosynthesis Vitamin B1 de novo: bacteria, some protozoa, plants and fungi. In particular, thiazolo and pyrimidine are produced separately and then Multi-function rooms to form thiamine monophosphate (ThMP) by the action of the enzyme thiamine phosphate synthase (EC2.5.1.3).

The biosynthetic pathways of vitamin B1 can differ between the various organisms. In E. coli and other Enterobacteria, ThMP can be phosphorylate to the cofactor thiamine diphosphate (ThDP) from an enzyme Chinese thiamine phosphate (ThMP + ATP → ThDP + ADP, EC 2.7.4.16). In most bacteria and eukaryotes, ThMP comes hydrolyzed in Thiamin, subsequently pyrophosphorylate in ThDP by the enzyme thiamine diphosphochinase (tiamina + ATP → ThDP + AMP, EC 2.7.6.2).



The biosynthetic pathways of vitamin B1 are regulated by riboswitch, that is through a short strand of RNA able to directly bind a small target molecule, and as an effect of this modular binding, the expression of a gene would take place. If there is a sufficient quantity of thiamine, this binds to the mRNA of the necessary enzymes and prevents their translation. If it is not present, there is no inhibition and the enzymes necessary for biosynthesis are produced. The specific riboswitch, the riboswitch TPP (or ThDP), is the only riboswitch identified is in eukaryotic organisms and prokaryotici.

functions

Functions of vitamin B1

Vitamin B1 feed it can have a coenzymatic or extracoenzymatic precursion function. It plays an indispensable role:

  • for the metabolic pathway of energy nutrients;
  • for the Develop area of mitochondrial membrane
  • for the function area of membrana synaptosomiale.

Note: we are talking about food B1 because, before the enzymatic catalyst action, it it is not active and it is considered a sort of "transport" of the final molecule.

All organisms use vitamin B1, but as we have said, it is produced de novo only by bacteria, fungi and plants. Animals have to get it from the diet; therefore, for man, it is a essential nutrient. Insufficient intake in birds produces characteristic polyneuritis.


Vitamin B1 phosphates are involved in many cellular processes. The plus form common and the pyrophosphate (o diphosphate) of thiamine (TPP), A coenzyme in catabolism of sugar and to the fundamental amino acids. In yeasts, TPP is also required in the first phase of alcoholic fermentation.

To date, five natural derivatives of thiamine phosphate are known: thiamine monophosphate (ThMP), thiamine diphosphate (ThDP) - also known as Thiamin pyrophosphate (TPP) - thiamine triphosphate (ThTP), theadenosine thiamine triphosphate (AThTP) e adenosine thiamine triphosphate diphosphate (AThDP).

While the role of the thiamine diphosphate coenzyme is well known and widely described, the action not coenzymatic of vitamin B1 and its derivatives is less known and probably related to some recently identified proteins that do not exploit the catalytic action of thiamine diphosphate.

Thiamine diphosphate or pyrophosphate

There is currently no known physiological role attributable to thiamine monophosphate (ThMP), unlike diphosphate, which is physiologically relevant.

The synthesis of thiamine pyrophosphate (TPP), also known as cocarboxylase, it is catalyzed by an enzyme called thiamine diphosphochinase according to the thiamine + ATP → ThDP + AMP reaction (EC 2.7.6.2).

ThDP is a coenzyme for various enzymes that catalyze the transfer of two carbon units and, in particular, the dehydrogenation (decarboxylation and subsequent conjugation with coenzyme A) of 2-oxoacids (alpha-ketoacids); eg:

  • In most species:
    • pyruvate dehydrogenase and 2-oxoglutarate dehydrogenase (also called α-ketoglutarate dehydrogenase)
    • Branched-chain α-ketoacid dehydrogenase
    • 2-hydroxytryptanoyl-CoA lyase
    • transchetolasi
  • Only in some species:
    • pyruvate decarboxylase (in yeasts)
    • several additional bacterial enzymes.

Transketolase, pyruvate dehydrogenase (PDH) and 2-oxyglutarate dehydrogenase (OGDH) enzymes are import anti in metabolism to the carbohydrates.

The cytosolic transketolase enzyme is a key element in the pathway pentose phosphates, main in the biosynthesis of pentose sugars ribosio e dissyribose.

Mitochondrial PDH and OGDH are part of biochemical pathways that generate adenosine triphosphate (ATP), a major form of energy for the cell.

La PDH fellow worker la glycolysis al cycle of citric acid, while OGDH catalyzes a slowdown in the citric acid cycle.

In the nervous system, PDH is also involved in production di acetylcholine (neurotransmitter) and in the synthesis of myelin.

Thiamine triphosphate

Thiamine triphosphate (ThTP) has long been considered a form neuroattiva specific to vitamin B1, as it plays an important role in chloride channels in mammalian and other animal neurons - although this role is not fully understood.

It has also recently been shown that ThTP is also present in bacteria, fungi, plants and other animals, suggesting a possible much larger cellular role. In particular, in Escherichia coli it appears to play a role in responding to the demand for amino acids.

Adenosine Thiamine Triphosphate

Adenosine thiamine triphosphate (AThTP) or thiaminylated adenosine triphosphate was recently discovered in E. coli, where it accumulates in carbon attraction. In these bacteria, AThTP can represent up to 20% of the total vitamin B1. It is also present in smaller quantities in yeasts, in the roots of higher plants and in various animal tissues.

Adenosine thiamine diphosphate

Adenosine thiamine diphosphate (AThDP) or thiaminylated adiamine diphosphate is present in small amounts in the liver of vertebrates, but its role remains unknown.

Alimony

Food sources of vitamin B1

- carrier foods of vitamin B1 are both of origin vegetable and animal; in particular: whole grains, legumes, some meats, offal and fishery products. Cereals are particularly rich in it fortified for breakfast.

Food fortification of vitamin B1

La refining of the grain, more precisely the elimination of the edible fibrous coating and of the embryo (germ), impoverishes notably vitamin B1 food.

In the United States, the shortages of vitamin B1 they became common in the first half of the twentieth century due to the exclusive use of white flour. The "American Medical Association" suggested restoring the content of these vitamins through the fortification of wheat, which started in the United States in 1939. The United Kingdom joined in 1940 and Denmark in 1953. As of 2016, some 85 countries had passed legislation requiring the fortification of wheat flour with certain nutrients and 28 % of the industrially ground flour was fortified with thiamin and other B vitamins.

for fortification food is used on sale mononitrato of thiamine instead of thiamine hydrochloride, as mononitrate is more stable and is not hygroscopic (does not absorb water), unlike hydrochloride. When thiamine mononitrate dissolves in water, releases nitrate (about 19% of its weight) and comes later absorbed like cation of vitamin B1.

Vitamin B1 degradation

Thiaminasi

In food vitamin B1 can be degraded in different ways. Sulfites, which are usually added as preservatives, attack the thiamine on the methylene bridge, cutting the pyrimidine ring from the thiazole ring. The speed of this reaction increases in condition acid.

Vitamin B1 can be degraded by thiaminesi thermolabile present in raw fish and shellfish. Some thiaminases are also produced by bacteria. Bacterial thiaminases are cell surface enzymes which, before being activated, must dissociate from the membrane; dissociation can occur in ruminants under acidotic conditions. Ruminant bacteria also reduce sulfate to sulfite, which is why an intake high di sulphate in the diet can have activity thiamine-antagonist.

Vitamin B1 antinutrients

The antagonists of thiamine vegetable are stable al heat and occur as ortho- and para-hydroxyphenols. Some examples are thecaffeic acid, L 'chlorogenic acid el 'acid tannic. These compounds interact with thiamine by oxidizing the thiazole ring, thus preventing its absorption.

Due flavonoids, quercetin e routine, are thiamine antagonists.

For further information: Foods with Vitamin B1

Absorption and Transport

Absorption of vitamin B1

Vitamin B1 is released by the action of phosphatase and pyrophosphatasi in the upper small intestine. At low concentrations, the process is carrier-mediated (active transport). At higher concentrations, absorption also occurs via passive diffusion. Active transport is greatest in the fasting and in 'ileo, but it can be inhibited from best before date di alcohol or from shortage di folate. The reduction dell 'absorption of vitamin B1 occurs a higher doses a 5 mg / the. On the serous portion of the intestine, the cellular release of the vitamin is ATPase Na + dependent.

Plasma transport of vitamin B1

Most of the circulating vitamin B1 is related to protein plasma, mainly all'albumin. About the 90% of total thiamine in the blood is found in erythrocytes. A specific was identified in rat serum binding protein called thiamine-binding protein (TBP) and is believed to be a conveyor regulated by hormones, important for distribution tissue of vitamin B1.

Cellular introduction of vitamin B1

L'assumption cellular of tissue vitamin B1 occurs for active transport e passive diffusion. About the80% of thiamine intracellular è phosphorylate and most of it is tied protein. Two SLC gene carrier proteins, SLC19A2 and SLC19A3 are capable of to carry vitamin B1. In some fabrics, theabsorption and secretion seem to be mediated from a conveyor soluble Na + dependent and on a gradients di protons transcellulari.

Distribution in the tissues of vitamin B1

Le stocks human thiamine are approx 25-30 mg, with greater concentration in the skeletal muscles, heart, brain, liver and kidneys. ThMP and free (non-phosphorylated) thiamine are present in plasma, milk, cerebrospinal fluid and, presumably, all extracellular fluid. Unlike the highly phosphorylated forms of vitamin B1, ThMP and free thiamine are capable of cross le cell membranes. The football and magnesium have been shown to to influence the distribution of thiamine in the body, and the shortage di magnesium aggravates la shortage of vitamin B1. The vitamin content in human tissues is lower to that of other species.

Excretion of vitamin B1

Thiamine and its acid metabolites (2-methyl-4-amino-5-pyrimidine carboxylic acid, 4-methyl-thiazole-5-acetic acid and thiamin acetic acid) are mainly excreted in the urine.

Need

Vitamin B1 requirement and intake recommendations

In the United States, Vitamin B1 "Estimated Average Requirements" (EAR) and "Recommended Dietary Allowances" (RDA) were updated in 1998 by the "Institute of Medicine" now known as the "National Academy of Medicine" (NAM).

The "European Food Safety Authority" (EFSA) refers to the collective set of information as "Dietary Reference Values", with "Population Reference Intake" (PRI) instead of RDA and "Average Requirement" instead of EAR. AI and UL are defined as in the United States.

For women (including those who are pregnant or breastfeeding), men and children the PRI is 0,1 mg of vitamin B1 for megajoule (MJ) of energy consumed. Since the conversion to kilocalories is: 1 MJ = 238,8 kcal, for an adult that consumes 2388 kcal should assume 1,0 mg / the of vitamin B1 - slightly lower than the US RDA. EFSA then reviewed the possible level of safety and concluded that there is insufficient evidence to establish a UL for vitamin B1.

LARNs advise healthy adults to take 0,4 mg of vitamin B1 every 1000 kcal introduced with the diet and di do not get off however below 0,8 mg. Pregnant women and nurses have a higher intake.

To promote adequate intake of micronutrients, pregnant women are often advised to to hire daily a multivitamin prenatal. While other micronutrient levels vary between different formulas, they all contain approx 1,5 mg of vitamin B1.

For food and supplement labeling purposes, in the United States the amount in a serving is expressed as a percentage of the daily value (% DV). For labeling purposes, 100% of the% DV vitamin B1 was rated at 1,5 mg, but as of May 27, 2016, it was revised to 1,2 mg to make it compliant with the RDA.

Shortage

Vitamin B1 deficiency

Synthetic vitamin B1 is commonly used to treat nutritional deficiency what if severe, may turn out fatal - especially in the infant.

In cases less severe, the signs not specific of vitamin B1 deficiency include: malaise, weight loss, irritability and confusion. The cases gravi instead, they lead to the so-called beriberi (beri-beri), Wernicke - Korsakoff syndrome, optic neuropathy, Leigh's disease, African seasonal ataxia e central pontine myelinolysis.

Pregnant women have a requirements top and then a greatest risk of shortage - even if the consequences are identical to those for the general population. This is probably due to the fact that vitamin B1 is sent preferably al fetus and placenta, specially during the third quarter of pregnancy. Those who suffer from iperemesi gravidarum have a higher risk.

In case of nursing and deficiency in the mother, vitamin B1 is administered directly in XNUMX cups milk maternal - even if that does not solve the deficit in nurse.

It has been speculated that the shortage of vitamin B1 plays a role in bad development of brain of child, which could lead to "sudden infant death syndrome" (SIDS) - sudden child death syndrome.

Vitamin B1 deficiency in the sick

in Western countries shortage of vitamin B1 occurs mainly inalcoholism chronic (alcohol abuse), with Wernicke's encephalopathy. They are at greater risk elderly, people with HIV/AIDS o diabetes mellitus type 2 and the people subjected to it bariatric surgery. Vitamin B1 deficiency has been associated with long-term use of diuretics ad high dosage, in particular furosemide - for the treatment ofheart failure.

For further information: Vitamin B1 and Alcoholism

Medical use

Medical use of vitamin B1

Vitamin B1 supplements and medications are typically taken for orally, but they can also be administered for injection intravenous or intramuscular. They can be used to prevent and treat vitamin B1 deficiency and related disorders, including beri-beri ed encephalopathy di Wernicke, but also the maple syrup urine disease and Leigh syndrome.

Vitamin B1 is available as a generic drug and as an over-the-counter drug. The wholesale cost in developing countries (as of 2016) is just under US $ 2,17 (USD) per 1g vial - about € 1,94 (€). In the United States, monthly therapy of a multivitamin containing vitamin B1 costs <$ 25.

Vitamin B1 is included in the list of "essential medicines"of the World Health Organization (WHO), the safest and most effective necessary for the health system.

Vitamin B1 supplements are generally well tolerated and alone repeated doses by injection can trigger allergic reactions.

Toxicity

Vitamin B1 toxicity

The intake of products containing vitamin B1 is also well tolerated, with the exception of the injections repeated (intravenous or intramuscular) which in some cases have resulted allergic reactions e anaphylaxis, nausea, lethargy e impairment area of coordination.

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