Phar 722Pharmacy Practice III

Vitamins-

Thiamin (B1)

Spring 2006

Thiamin (B1) Study Guide

• The applicable study guide items in the Vitamin Introduction

• History

• Structures including commercial forms of the vitamin

• Conversion to the cofactor form

• Function and cofactor including the specific types of reactions

• Commercial forms of the vitamin

History• After 26 years of constant research, the vitamin

preventative of the disease beri-beri has been isolated, its chemical constitution determined and the vitamin itself synthesized at a cost far lower than that of recovering it from bran.– --Scientific American, February 1938; reprinted in 258, 12

(Feb. 1988)

• Beriberi is based on a Chinese term. Sailors in the Japanese navy experienced thiamin deficiencies when fed rice in which the polishings had been removed to prevent mold growth. This is somewhat analogous to removing the germ from wheat in order to prolong the shelf life of flour containing foods.

Chemistry• Thiamin consists of a pyrimidine joined to a

thiazole ring by a methylene bridge. The thiazole nitrogen is a quaternary with a permanent positive charge. – There are two commercial salts.

• Thiamin hydrochloride is, in reality thiamin chloride hydrochloride. It is a double salt consisting of an amine hydrochloride on the pyrimidine amine and a chloride on the thiazole quaternary nitrogen.

– The double salt is very water soluble (1 gm/1ml) and, unfortunately, very hygroscopic.

• Thiamin nitrate is correctly named in that the nitrate anion is found on the quaternary nitrogen, and the pyrimidine amine is not protonated.

– The mononitrate is non-hygroscopic and still has good water solubility (1 gm/35 ml).

N

NH3C

CH2

N+

S

CH3

CH2

NH2

NO3-

Thiamine Mononitrate

CH2 OH

N

NH3C

CH2

N+

S

CH3

CH2

NH3+ Cl-

Cl-

Thiamine HCl(Thiamine Chloride HCl

CH2 OH

Hydroscopic;Sol: 1 gm/mlUses: parenterally& oral liquids.

Non-hygroscopic’Sol: 1 gm/mlUses: dry oral dosage forms.

Thiamin Uptake and Metabolism• An active transport system provides efficient

uptake of the vitamin into the intestinal mucosa cell.

• A thiamin kinase in the intestinal mucosa cell transfers a pyrophosphate from the ATP to the propyl alcohol at position 5 of the thiazole ring forming thiamin pyrophosphate. – The latter product is the cofactor form of the

vitamin. – There is some evidence that this phosphorylation

is the rate limiting step and controls the absorption of the vitamin.

– The cofactor is then transported to the necessary tissues.

N

NH3C

CH2

N+

S

CH3

CH2

NH3+ Cl-

Cl-

N

NH3C

CH2

N+

S

CH3

CH2

NH3+

Thiamine HCl(Thiamine Chloride HCl

Thiamine Pyrophosphate (TPP)(active coenzyme form)

CH2 O P O P O-

O O

O- O-

CH2 OH

ATP

AMP

Thiaminekinase

Intestinal mucosa;Possibly the rate limitingstep.

Cofactor Role-1• Oxidative decarboxylations of α-

ketoacids.– The cofactor form of thiamin is required for

all oxidative decarboxylations of α-ketoacids.• The most significant of these

– Pyruvate to acetyl CoA – α-Ketoglutarate to succinyl CoA – Methioninie and the three nonpolar amino acids, valine,

leucine, and isoleucine, also have an oxidative decarboxylation as part of their degradative metabolism.

R

CH2

N+

CS

CH3

CH2CH2OPP

H

R

CH2

N+

C-S

CH3

CH2CH2OPP

TPPTPP carbanion

R C C O-

O O

H+

R

CH2

N+

CS

CH3

CH2CH2OPP

C

C

O-

R

HO

O

CO2

R

CH2

N:

CS

CH3

CH2CH2OPP

C

R

OH

R

CH2

N+

CS

CH3

CH2CH2OPP

C-

R

OH

R

CH2

N+

CS

CH3

CH2CH2OPP

C

R

OH

H+

H

R C H

O

Cofactor Role-2• Transketolase Reaction

– Catalyzed transfer of two carbon fragments in the pentose phosphate pathway.

• The thiamin RDA is based on the amount of carbohydrate in the diet.

R

CH2

N+

C-

S

CH3

CH2CH2OPPR

CH2

N+

CS

CH3

CH2CH2OPP

H

R

CH2

N+

CS

CH3

CH2CH2OPP

CHO CH2OH

C

C

CH2OP

O H

H OH

H

TPPCH2OH

C

C

C

CH2OP

O

HO H

H OH

O H

CH2OP

H OH

R

CH2

N

CS

CH3

CH2CH2OPP

C-

HO

CH2OH

R

CH2

N+

CS

CH3

CH2CH2OPP

C-

HO

CH2OH

CH2OP

C

C

C

C

H OH

OHH

H OH

HO H

C

CH2OH

O

CH2OP

C

C

C

C

H OH

OHH

H OH

O H

TPP carbanion

Xylulose-5-P

H+

+

Glyceraldehyde-3-P

Sedoheptulose-7-P

Ribose-5-P

Possible Non-cofactor Role

• Based on animal studies, there is evidence that thiamine pyrophosphate (TPP) may be required for proper function of the ion channels in nerve conduction.– This may explain some of the neurological

symptoms seen with thiamin deficiencies.

Thiamin Deficiency-1• Beriberi.

– Wet beriberi • Edema resulting from a diseased heart

– Dry beriberi • Peripheral neurological symptoms.

– Cerebral beriberi (Wernicke-Korsakoff Syndrome)

– The wet and dry conditions are reversible upon administration of thiamin supplements. Reversibility of cerebral beriberi is dependent on the degree of brain damage.

– Thiamin deficient individuals can experience a variety of symptoms.

Thiamine Deficiency-2• Thiamin deficiencies are seen in chronic

alcoholism. It is thought that chronic ingestion of alcoholic beverages somehow inhibit thiamin uptake by the mucosal cell or possibly interfere with conversion to the cofactor form.

• It has been routine for many emergency rooms to include thiamin when administering an IV to an unconscious patient caused by improper drug use. It is assumed that these patients also suffer from chronic alcoholism and are experiencing Wernicke-Korsakoff Syndrome (cerebral beriberi), a form of thiamin deficiency.

Thiamin Deficiency-3• In November 2003, a German manufacturer of

a soy-based infant food formula sold a product lacking thiamin in Israel. – There were six cases of severe neurological

conditions including two infant deaths. – The company made the following mistakes in

formulating this new product (4 executives were dismissed):

• The analysis data for the new soy-based formula was wrongly interpreted with the result that thiamin was not added. The final product only contained 10 percent of the amount stated on the label. (It was mislabeled!)

• Although sent to an outside laboratory for testing, the fact that the analysis came back with the vitamin content missing was ignored.

• When it finally was discovered that the vitamin analysis was missing, there was no follow-up inquiry.

Hypervitaminosis Thiamin

• The vitamin is considered very safe.

• Possibly the rate limiting phosphorylation step in the intestinal mucosa reduces the risk of toxicity.

• Estimated toxic dose: 300 mg– There is no UL.

Dosage Forms• Most of the commercial forms of the vitamin

are synthetic.

• Thiamin Hydrochloride– Very water soluble (1 gm/1 ml)– Very hygroscopic - making it difficult to use in dry

formulations.– Commonly used in liquid preparations including

parenterals.

• Thiamin Mononitrate– Solubility: 1 gm/35 ml– Non-hygroscopic - making it the salt of choice for

dry dosage forms.

DRIs-1• Thiamin requirement parallel carbohydrate

intake.• AI

– Infants 0.2 - 0.3 mg/day

• EAR– Children (1 - 13 years) 0.4 - 0.7 mg/day– Males (14 - 18 years) 1.0 mg/day– Females (14 - 18 years) 0.9 mg/day– Men (19 - 50+ years) 1.0 mg/day– Women (19 - 50+ years) 0.9 mg/day– Pregnancy 1.2 mg/day– Lactation 1.2 mg/day

DRIs-2• RDA

– Children (1 - 13 years) 0.5 - 0.9 mg/day– Males (14 - 18 years) 1.2 mg/day– Females (14 - 18 years) 1.0 mg/day– Men (19 - 50+ years) 1.2 mg/day– Women (19 - 50+ years) 1.1 mg/day– Pregnancy 1.4 mg/day– Lactation 1.5 mg/day

• UL– None reported

Food Sources

• Beans

• Nuts

• Fruits

• Cereal grain germs

• Spinach

• Meat

• (Animals have to obtain thiamin from plants or eating other animals.)