Phar 722 Pharmacy Practice III

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Phar 722Pharmacy Practice III

• Vitamins-
• Vitamin E Family
• Spring 2006

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Vitamin E Study Guide

• The applicable study guide items in the Vitamin
  Introduction
• History
• Structure of the active and commercial forms
• Transport of the vitamin
• Compare and contrast vitamin deficiencies in
  humans relative to animals
• Role of structurely related compounds
• Hypervitaminosis E
• Approaches to formulation

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Vitamin E History

• 1922
• Evans and Bishop showed that rats maintained on
  certain diets did not produce offspring.
• These same rats seemed normal in all other
  respects including physical growth.
• The condition could be corrected by addition of
  lettuce, whole wheat, and cereal grains.
• Later it was shown that the vitamin activity was
  in certain wheat germ oils.

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Vitamin E Chemistry-1

• The tocopherols and tocotrienols are natural
  antioxidants found in vegetable oils.
• Historically, they were removed during the
  refining process.
• Of course this means that the refined products
  are subject to oxidative spoilage. Therefore,
  the manufacturers add antioxidants back into the
  products.
• These may be tocopherols or synthetic compounds.
  
• Tocopherols are widely used as antioxidants in
  prepared foods.
• The milling companies are major suppliers of
  tocopherols extracted from the wheat germ.

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Vitamin E Chemistry-2

• Tocopherol means child bearing alcohol.
• tokas - child
• phero - to bear
• ol alcohol
• The chemistry is complex.
• There are a family of tocopherols, with
  a-tocopherol showing the most specific vitamin
  activity based on a rat fertility assay.
• Consensus is developing that vitamin E should be
  defined as 4 tocopherols and 4 tocotrienols.

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Vitamin E Chemistry-3

• The stereochemistry is very important!
• There are three chiral centers (position 2 on the
  chroman ring and positions 4' and 8' on the
  phytyl chain. This means that eight isomers are
  possible.
• The normal situation seen with vitamins that
  have two or more stereoisomers is only one isomer
  is active. Thus a racemic (usually represented
  as d,l) mixture contains 50 of the activity
  compared with an equi-molar amount of the active
  isomer.

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Vitamin E Uptake

• Bile (conjugated bile salts) is essential for
  absorption.
• The vitamin usually is present in food or vitamin
  supplements as an ester. This is hydrolyzed in
  the intestinal tract. The free tocopherol
  becomes part of the mixed micelles. Absorption
  is 35-85 efficient.
• Entry into the body is made on the chylomicrons
  by the lymphatic system. The vitamin is
  transported throughout the body on chylomicrons,
  VLDL, LDL, and HDL. It is distributed in adipose
  tissue, liver and muscle.
• There is evidence that transport across the
  intestinal mucosa cells followed by incorporation
  into chylomicrons may favor RRR a-tocopherol
  because of an a-tocopherol transfer protein.
• The natural RRR isomer is preferred for
  incorporation into very low density lipoprotein
  (VLDL).
• The tocopherols can be considered natures oil
  soluble anti-oxidant in both plants and animals
  with animals, including humans, obtaining the
  vitamin from plants.

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Vitamin E Deficiencies-1

• There has been a considerable mystique that
  surrounds this vitamin.
• There doesn't seem to be a defined deficiency
  syndrome in humans for which there is a parallel
  model in animals.
• To put it another way, there is no valid animal
  model that can be extrapolated into humans.
• The next slide shows one classification system
  for tocopherol deficiencies.

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Vitamin E Deficiencies in Animals and Humans

• Vitamin E Deficiencies Seen in Animals
• Reversible reproductive failure in the female
  rat.
• Irreversible degeneration of rat testicular
  tissue.
• Nutritional muscular dystrophy in monkeys,
  rabbits, guinea pigs, lambs, calves, turkeys and
  chicks.
• Anemia in monkeys.
• Vitamin E deficiency seen in humans (Most
  reported deficiencies are caused by problems with
  fat absorption.)
• A partially reversible set of neurological
  problems.
• Hemolytic anemia in premature infants.

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Vitamin E Deficiencies-2

• In summary, there seems to be a general
  antioxidant role and a specific function in the
  cell's oxidation-reduction systems. This may
  complement some of the functions attributed to
  glutathione.
• There has been considerable debate as to whether
  the RRR isomer is the only biologically active
  form of the vitamin. The synthetic form of the
  vitamin is a mixture of all eight stereo isomers
  (now referred to as rac-a-tocopherol rather than
  d,l-a-tocopherol).
• Many of the research articles reporting on the
  effectiveness of vitamin E use commercial
  products which usually have a mixture of isomers
  and dont have any tocotrienols.
• Recently, there is debate as to whether the a and
  ? forms have different in vivo activities.
• ?-Tocopherol is the predominant dietary form.
• But a-tocopherol may displace the ?-isomer.
• Because there are both general and
  stereo-specific antioxidant activities, the RDA
  tables state that the activity ratio of
  RRR-a-tocopherol to rac-a-tocopherol is 1 to
  1.36.

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Vitamin E Deficiencies-3

• Complicating these evaluations further is the
  observation that an in vitro comparison of the
  antioxidant activities of a-, ß-, ?-, and
  d-tocopherols is not parallel with in vivo
  vitamin results in rats.

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Vitamin E Deficiencies-4

• The in vivo rat fetal rankings for the
  tocopherols are
• a gt ß gt ? gt d
• Depending on the solvent, the in vitro
  antioxidant rankings can parallel the in vivo.
  When carrying out the evaluation in fats and
  oils, the in vitro rankings are
• d gt ? ß gt a
• All isomers are antioxidants and probably do
  provide general antioxidant protection internally
  or in vivo. On the other hand, evidence points
  to the RRR isomer as being specific for a variety
  of reductase systems, possibly involving selenium
  (Se) and glutathione (GSH/GSSG). The "Relative
  Biological Activity" in the previous table is
  based on a rat resorption-gestation assay.
• The next two slides illustrate how the tocopherol
  family might function as antioxidants.

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Possible Vitamin E Antioxidant Mechanism
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Possible Free Radical Antioxidant Mechanism
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Vitamin E Deficiencies-5

• Consistent with antioxidant model, the RDA is
  based on the polyunsaturated fatty acid (PUFA)
  consumption. The implication is that, if a
  increased PUFA intake is recommended, the RDA for
  tocopherol should be increased.
• The hemolytic anemia seen in premature infants is
  one of the few specific nutritional deficiencies
  seen in humans.
• Because of poor placental transfer, newborn have
  little of the vitamin. Human milk contains 2 - 5
  mg/liter. Cow's milk contains less.

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Current Information on Vitamin E

• ?-Tocopherol is the most common form in the U.S.
  diet, but a-tocopherol is the most common form
  found in the blood.
• In the blood on lipoproteins (VLDL, LDL, etc.)
• a-Tocopherol may be more effective than
  ?-tocopherol in protecting against prostate
  cancer. This may be more effective in smokers.
• See food lists for distribution of the a and ?
  forms.
• Some evidence that vitamins C and E, zinc and ,
  but not ß-carotene, help patients with early
  signs of age-related macular degeneration.
• Current trial involving these nutrients plus
  selenium underway.
• Meta-analysis show no risk reduction for
  myocardial infarction, stoke or cardiovascular
  death.
• Some studies show increased oxidant activity with
  doses above 400 IU.
• Vitamin E did not slow the progression of
  Alzheimers Disease.

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Hypervitaminosis E

• This is a relatively safe vitamin.
• But toxicities have been reported involving
  chronic administration of 300 1200 mg per day.
  
• The symptoms can be very serious and include
  thrombophlebitis, pulmonary embolism,
  hypertension, breast development in men and
  children, severe fatigue, and nonmalignant breast
  tumors.
• In 2004, there were news reports that high doses
  (2000 IU/day) of vitamin E slowed the progression
  of Alzheimers Disease. What the news failed to
  report was that a diet rich in foods containing
  vitamin E may help protect some people against
  Alzheimers Disease.
• There are at least five ongoing studies examining
  the role of antioxidants in delaying onset of
  Alzheimers Disease.

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Dosage Forms

• Stability
• The tocopherols, being antioxidants, are very
  sensitive to oxygen. Sensitive to UV light is
  another problem. There are two provitamin esters
  that are used commercially.
• Acetate
• used in oils, emulsions, gelatin matrices, etc
• Hemisuccinate
• Used in dry dosage forms requiring a free flowing
  powder. In theory, the sodium salt would be
  water soluble enough for aqueous injections.

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Vitamin E Dosage Forms
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DRIs (based on a-tocopherol)-1

• AI
• Infants (0 - 12 months) 0.6 mg/kg/day
• EAR
• Children (1 - 8 years) 5 - 6 mg/day
• Boys (9 - 18 years) 9 - 12 mg/day
• Girls (9 - 18 years) 9 - 12 mg/day
• Men (19 - 50 years) 12 mg/day
• Women (19 - 50 years) 12 mg/day
• Men (51 - 70 years) 12 mg/day
• Women (51 - 70 years) 12 mg/day
• Pregnancy 12 mg/day
• Lactation 16 mg/day

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DRIs (based on a-tocopherol)-2

• RDA
• Children (1 - 8 years) 6 - 7 mg/day
• Boys (9 - 18 years) 11 - 15 mg/day
• Girls (9 - 19 years) 11 - 15 mg/day
• Men (19 - 50 years) 15 mg/day
• Women (19 - 50 years) 15 mg/day
• Men (51 - 70 years) 15 mg/day
• Women (51 - 70 years) 15 mg/day
• Pregnancy 15 mg/day
• Lactation 19 mg/day

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DRIs (based on a-tocopherol)-3

• UL
• Infants Not established (Do not give
• supplements use only food and
• formula for sources.)
• Children 200 mg/day (1 - 3 years) up to
• 600 mg/day (9 - 13 years)
• Adolescents 800 mg/day
• Adults (19 years) 1,000 mg/day
• Pregnancy 800 - 1,000 mg/day
• Lactation 800 - 1,000 mg/day

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Food Sources-1

• a-Tocopherol
• Almonds, hazelnuts, sunflower seeds
• Spinach
• Olive oil, canola oil
• ?-Tocopherol
• Soybean oil, corn oil
• Tocotrienols
• bran and germ fractions of certain seeds and
  cereals

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Food Sources-2