Phar 722 Pharmacy Practice III Vitamins- Ascorbic Acid (C) Spring 2006.

Phar 722Pharmacy Practice III

Vitamins-Ascorbic Acid (C)

Spring 2006

Ascorbic Acid (C) Study Guide

• The applicable study guide items in the Vitamin Introduction

• History• Structures of both forms• Salt formation• Major routes of degradation and how to

minimize them• Metabolic functions• Deficiency condition• Use of ascorbic acid esters• Commercial forms of the vitamin

Ascorbic Acid History-1• In this best-fed nation in the world, one-third

to one-half of the population lacks vitamin C. This vital food element-essential for vigor and efficiency-is now available in a new mass-produced synthetic form. Technicians have developed successful manufacturing processes based on combining ascorbic acid and sodium in water-free methyl alcohol. The new vitamin C is precipitated as a pure, white crystalline mass.– Scientific American, reprinted from an article

published November 1946, November, 275 (5) 10, 1996.

Ascorbic Acid History-2• 1498 - After about 10 weeks as sea, Vasco da Gama's

crew experienced a new illness which caused ...their feet and hands swelling and their gums growing over their teeth so they could not eat. – The crew recovered within a week after eating oranges

purchased in East African ports. – The illness reoccurred on the voyage back which, again,

responded to fresh oranges. About half the crew died at sea from scurvy.

• 1530s - Jacques Cartier, who explored the St. Lawrence River in Canada, lost sailors to scurvy until the local Indians explained how the use of a tea made from birch bark cured the disease.

• Chemical and Engineering News, Indians in Canada used birch bark tea for scurvy, Chemical and Engineering News, February 19, 1991, p. 56.

Ascorbic Acid History-3• Scurvy became the worst of the occupational

illnesses because approximately 2,000,000 million sailors died from the disease over the next 300 years.

• Large numbers of African slaves also died during transport from Africa to the Americas.

• 1747– Dr. James Lind, a British naval surgeon, reported

on an experiment where he tried various treatments for scurvy while aboard a ship.

• These ranged from oranges and lemons, to drinking seawater daily, to using vinegar with each meal.

• Only the patients on oranges and lemons improved.

Ascorbic Acid History-4• Forty years later the British Navy finally began issuing

0.75 oz of lime or orange juice per day to the sailors. The East India Company also followed this procedure.– By the 1850s, most commercial sailing vessels used steam.

• The result was faster trips and fresher food for the crew. Scurvy ceased to be a problem among sailors.

• Dr. Lind was a very dedicated and intelligent naval surgeon. – He recommended shipboard delousing methods like those used

today to combat typhus, suggested the use of hospital ships for sick sailors in tropical ports, and in 1761 arranged for shipboard production of drinking water by distillation.

Ascorbic Acid History-5• Scurvy on land - This was seen in convicts, the

California gold miners, prisoners of war, Irish farmers deprived of fresh potatoes (a good source of vitamin C) during the potato blight, Arctic explorers, populations in cities under long term siege, etc.– Barlow's Disease - scurvy in infants.

• It resembles adult scurvy except that infants don't have any teeth to lose.

• It was common in during the late-Victorian periods and affluent London and New York mothers bottle-fed their infants. The product was acceptable except for its lack of Vitamin C.

– Breast-fed infants generally do not get scurvy because the maternal milk can contain up to seven times the ascorbic acid concentration of maternal blood plasma.

– Because of this fact, scurvy was not seen in infants in czarist Russia even though it was endemic among the adult peasant population.

• Scurvy became a disease among the affluent in the late 19th century particularly due to the pasteurization of milk used in infant formula.

Ascorbic Acid History-6

• 1907– A paper was published by two researchers

who were investigating beriberi reported that guinea pigs fed solely on grain developed scurvy.

• This was the first report of an animal model for this nutritional disorder.

• 1932 – Ascorbic acid was isolated

Ascorbic Acid Chemistry• In theory, either the reduced or oxidized

form of the vitamin is effective. – In practice, the oxidized vitamin C is very

unstable with hydrolysis of the lactone ring the site of degradation.

– This is why vitamin C activity can decrease in a pitcher of orange juice over time, particularly at room temperature.

• The D-isomer has no vitamin activity, but it can be used as an antioxidant in foods.

OO

OHHO

C

CH2OH

H

[O]

[H]

H2O

OHO

OO

C

CH2OH

HO-

OO

OO

C

CH2OH

OH

Na+

OO

OH-O

C

CH2OH

H

L-Ascorbic Acid Dehydro-L-Ascorbic Acid

pKa 4.2 pKa 11.6

Sodium L-Ascorbate

L-2,3-Diketogluonate

HO

HO

HO HO

Ascorbic Acid Chemistry-2

Why Is Ascorbate Essential?• Ascorbic acid is not a vitamin in most

animals.

• It is synthesized from glucose.

• Humans, other primates and guinea pigs lack the ability to make L-gulonlactone and then oxidize it to ascorbic acid.

• Why would humans not have this enzyme?

Ascorbic Acid BiosynthesisCO2

-

CH

CH

HC

CH

CH2OH

HO

HO

OH

HO

CH

CH CH

OO

OHHO

C

CH2OH

H

H2O

[2 H]

O

OH

OH

CO2-

OH

OH

CH

C C

OO

OHHO

C

CH2OH

H

O

OH

OH

CH2OH

OH

OH

D-Glucose

Several

Steps

D-Glucuronate

1

66

1

L-Gulonic Acid

6

1

L-Gulonolactone

Glucuronatereductase

NADPH + H+ NADP+

Aldono-lactonase

Gulonolactoneoxidase

L-Ascorbic Acid

HOHO

Pentose Phosphate Pathway Humans and primates

Ascorbate Uptake and Metabolism

• Surprisingly, little is know about the details of the uptake and distribution of this vitamin.

• Little is known about its pharmacokinetics.

• Little is known about its storage.

Biochemical Functions• The vitamin is required for many reactions

involving oxidations. These include:– Tyrosine metabolism (phe → tyr)– Formation of hydroxyproline from proline– Formation of hydroxylysine from lysine– Synthesis of carnitine (required for fatty acid

transport)– Reduction of folic acid to tetrahydrofolate– Antioxidant in the tissues. (protect vitamin A;

reduce C-reactive protein levels indicating anti-inflammatory properties.)

– Hydroxylation of steroids in the adrenal gland forming hydrocortisone and cortisone.

– Formation of bile acids from cholesterol.

Ascorbic Acid Deficiency

• Scurvy (anti-scorbutic vitamin) and Barlow’s Disease– Scurvy is a degeneration of the connective

tissues probably related to the inability to form the hydroxylated amino acids seen in cartilage, elastin and other related proteins.

• The result is the hemorrhaging, loss of teeth, improper bone growth, etc.

Antioxidant Role of Vitamin C• The DRIs are based on prevention of scurvy.• Vitamin C also is a water-soluble antioxidant.• Should humans take larger amounts of ascorbate to prevent or

reduce the severity of:– Common cold?– Malignancies?– Diabetes mellitus– Cardiovascular disease.

• The results are mixed.• The vitamin, along with lipid-soluble vitamin E, appears to be

beneficial in smokers.• Vitamins C and E do not reduce the risk of preeclampsia

hypertension and proteinuria during pregnancy, the risk of intrauterine growth restrictions or the risk of death or other serious outcomes in their infants.

Hypervitaminosis C-1• This appears to be a very safe vitamin as

evidenced by individuals take megadoses for a variety of anecdotal reasons.

• When vitamin C became popular after Linus Pauling’s book advocating megadosing of the vitamin, early manufacturing was sloppy producing products high in sodium.– This led to the FDA requiring manufacturers to list

the sodium content on the label.– This led the manufacturers to clean up their

product.

Hypervitaminosis C-2• There have been some problems seen when

people suddenly reduce their intake from the megadoses to the levels of its RDA. – The patient's metabolism is geared up to

eliminating the large amounts of excess vitamin. Sudden cessation of vitamin intake might cause a transient deficiency. (Anecdotal)

– This may be most serious in infants. Babies born from mothers who have been taking large doses of Vitamin C can show clinical signs of scurvy because they are capable of metabolizing the large doses that crossed the placental barrier.

– These children may have to be withdrawn from the vitamin over a period of time. (Anecdotal)

Ascorbic Acid Dosage Forms-1• Most of the vitamin is made

synthetically from glucose to maintain stereochemistry. – Does that mean that synthetic ascorbic

acid is natural?

• There is a big market for the vitamin. – Takeda U.S.A. has a $90 million Vitamin C

plant in Wilmington, NC which has the capacity to produce 11 million lb per year.

– A plant formerly owned by Roche can produce 30 million lb per year.

Ascorbic Acid Dosage Forms-2The sodium salt is usually used for the parenteral dosage forms.The palmitic acid ester is found in oral dosage forms and oil-based dosage forms.

OO

OHHO

C

CH2OH

H

L-Ascorbic Acid

HO

Na+

OO

OH-O

C

CH2OH

H

Sodium L-Ascorbate

HO

OO

OHHO

C

H2C

H

L-Ascorbic Acid Palmitate

HO

O C(CH2)14CH3

O

Ascorbic Acid DRIs-1• AI

– Infants 40 - 50 mg/day

• EAR– Children (1 - 8 years) 13 - 22 mg/day– Boys (9 - 18 years) 39 - 63 mg/day– Girls (9 - 18 years) 39 - 56 mg/day– Men (19 - 70+ years) 75 mg/day– Women (19 - 70+) 60 mg/day– Pregnancy 66 - 70 mg/day– Lactation 96 - 100 mg/day

Ascorbic Acid DRIs-2

• RDA– Children (1 - 8 years) 15 - 25 mg/day– Boys (9 - 18 years) 45 - 75 mg/day– Girls (9 - 18 years) 45 - 65 mg/day– Men (19 - 70+ years) 90 mg/day– Women (19 - 70+) 75 mg/day– Pregnancy 80 - 85 mg/day– Lactation 115 - 120 mg/day

Ascorbic Acid DRIs-3• UL

– Infants Not established;

use formula and food only

– Children (1 - 8 years) 400 - 650 mg/day– Boys & Girls (9 - 13 years) 1,200 mg/day– Adolescents (14 - 18 years) 1,800 mg/day– Pregnancy 1,800 - 2,000 mg/day– Lactation 1,800 - 2,000 mg/day– Adults (19+ years) 2,000 mg

Food Sources

• Citrus fruits

• Berries

• Broccoli

• Green cabbage

• Potatoes