III. FACTORS AFFECTING MICRONUTRIENT NEEDS

Table 6



Drugs That Influence Vitamin Use



Drug Class

Diuretics

Spironolactone

Thiazide

Bile acid sequestrant

Cholestyramine

Colestipol

Laxative

Phenolphthalein

Anticonvulsant

Phenytoin

Anticoagulant

Coumarin, decoumarol

Warfarin

Immunosuppressant

Cyclosporin

Antibacterial

Isoniazid

Sulfasalazine

p-Aminosalicylic acid

Neomycin

Tetracycline

Anti-inflammatant

Phenylbutazone

Chelating agents

EDTA

Penicillamine

Thiosemicarbazide

Anticholinergic

L-DOPA

Antihypertensive

Hydralazine

Antimalarial

Pyrimethamine

Antineoplastic

Methotrexate

Antihistamine

Ametidine

Theophylline

Antacids

Aluminum hydroxide

Magnesium hydroxide

Sodium bicarbonate

Other

Ethanol

Mineral oil



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Nutrient Affected

Vitamin A

Potassium

Vitamin A, Vitamin B12, folacin

Vitamin A, Vitamin K, Vitamin D

Vitamin A, Vitamin D, Vitamin K, potassium

Vitamin D, Vitamin K, folacin

Vitamin K



Vitamin K

Niacin, B6

Folacin

Vitamin B12

Vitamin B12

Calcium, magnesium, iron, zinc

Niacin

Calcium, magnesium, lead

Copper, Vitamin B6

Vitamin B6

Vitamin B6

Vitamin B6

Folacin

Folacin

Vitamin B12

Protein

Folate, phosphate

Phosphate

Folacin

Niacin, folacin, thiamin

Vitamin A, β-carotene



UNIT



2



Integration of the Functional Aspects

of Vitamins and Minerals

TABLE OF CONTENTS

I. Overview

II. The Role of Micronutrients in Gene Expression

III. Synthesis of Purines and Pyrimidines

IV. Micronutrients as Stabilizers

Supplemental Readings



I. OVERVIEW

At the turn of the century, scientists seeking to understand the role of diet in health maintenance

began to use rats in their research on nutrient needs. When these animals were fed diets consisting

of purified proteins, fats, and carbohydrates, they died. It was soon found that specific minerals

and additional factors, termed accessory food factors by Hopkins, were present in an unrefined diet

and were necessary to sustain life. The minerals and these “accessory factors” were needed in very

small amounts. Because it was thought that the “accessory factors” all contained nitrogen, they

were called amines. Casimir Funk, an early nutrition scientist, coined the term “vitamines” to

indicate that these amines were vital to the survival of the animal. Later, after it was discovered

that not all vitamins contained amines, the final “e” was dropped from the word.

Vitamins are a large group of potent organic compounds necessary in minute amounts in the

diet. They are usually divided into two classes based on their solubility characteristics. The watersoluble vitamins are soluble in water and usually function as coenzymes in the metabolism of

protein, fats, and carbohydrates. The fat-soluble vitamins are not usually soluble in water but are

soluble in one or more solvents such as alcohol, ether, or chloroform.

Each of the vitamins has a specific chemical structure and many can be synthesized rather

inexpensively. Thus, multivitamin supplements can be purchased in drugstores for a modest price.

While specific vitamins can cure specific deficiency diseases, as indicated in Unit 1 and detailed

in the sections on each of the vitamins, the use of supplements by people consuming a wide variety

of raw and cooked foods may be unnecessary.

Before the vitamins were chemically isolated and described, scientists began naming the

compounds. In some instances, different research groups were studying the same compound and



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unwittingly gave different names to the same vitamin. This contributed confusion to the identity

of vitamins. Frequently, the name chosen described the food source or the deficiency symptom.

Thus, for years thiamin was known as the antiberiberi factor, vitamin K was known as the coagulation factor, and vitamin E as the wheat germ factor or the antisterility factor. As nutrition scientists

began publishing their findings, it became important to establish a uniform nomenclature and one

based on the alphabet was devised. Compounds having vitamin activity were alphabetized in order

of their discovery. Now, however, information about the vitamins has expanded to such an extent

that this nomenclature system is outmoded. Chemically descriptive terms are now being used that

more correctly identify the vitamin in question. Nonetheless, alphabetical designations are still

being used and the reader will encounter some of these in this text.

As scientists learned more about the vitamins they began to reclassify them according to function

rather than solubility. Thus, we have vitamins that serve as membrane stabilizers, as coenzymes,

or that have antioxidant properties and/or that act at the genomic level. Some vitamins fall into

more than one category. For example, ascorbic acid serves as a general antioxidant, as a redox

agent (as a substrate being oxidized to dehydroascorbic acid), and yet also acts at the levels of

transcription and translation for the protein, procollagen. Vitamin A is another one that is multifunctional. It has a direct role in the visual cycle, is an antioxidant, stimulates the RNA transcription

for the retinoic acid receptor, and when bound to this receptor serves as a transcription factor for

the transcription of numerous mRNAs. As the reader progresses through the units and sections

devoted to the individual vitamins, this multifunctionality will be described.

Similarly, as the roles for each of the minerals were elucidated, the minerals likewise were

subdivided into two groups based not on solubility characteristics but on the magnitude of need.

Thus, we have the macrominerals and the microminerals. The human need for the former is much

greater per day than the need for the latter. Just as some vitamins can serve as coenzymes in

intermediary metabolism, minerals serve as cofactors in many of these same reactions. Vitamins

and minerals both have active roles in the formation and maintenance of the body’s structure as

well as its function. Minerals and vitamins are essential to the regulation of metabolism and, as

well, are important components for the expression of many specific genes.



II. THE ROLE OF MICRONUTRIENTS IN GENE EXPRESSION

Among the many functions that vitamins and minerals serve in the body, one stands out in its

primacy. That is, the service in gene expression. Almost every micronutrient is involved either

directly as part of a cis- or trans-acting factor in RNA transcription, or as an important coenzyme

in the synthesis of the purine and pyrimidine bases, or as a coenzyme in intermediary metabolism

which provides substrates and energy for the support of cell replication, cell growth, DNA replication, RNA transcription, RNA translation, and protein synthesis. Figure 1 illustrates the process

of gene expression and Table 1 itemizes specific effects of vitamins and minerals on this process.

Some of these effects are direct, some are indirect. Many of the symptoms of vitamin deficiencies

can be traced to this involvement in gene expression. Gene products and cell types with very short

half-lives will be among the first to be affected by the absence of a given micronutrient. Hence,

skin lesions are a frequent feature of the deficient state because epithelial cells have an average

half-life of 7 days. Red blood cells have an average half-life of 60 days and many nutrient deficiencies are characterized by anemia. Similarly, vitamin- and mineral-dependent gene products

(enzymes, receptors, transporters) also will be affected should that particular nutrient be in short

supply. Conversely, we have instances of diversity within a population such that one individual’s

nutrient intake is fully adequate while another individual in the same population, consuming that

same amount of that same nutrient, is in the deficient state. This contrast is due to individual genetic



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Figure 1



Overview of gene expression.



variability and can be found in every species and strain of living creatures. The explanation for

this variability, not only in nutrient needs and tolerances but also in such characteristics as skin

color, height, weight, or any of the myriad characteristics that distinguish one species from another

and one individual from another, is in the genetic material, DNA.

The mammalian genome contains 4 × 109 base pairs (bp) and exists as a double-stranded helix

with the purine and pyrimidine bases arranged in a preordained sequence and held together by

phosphate and ribose groups. There is far more DNA in each cell than is used. In contrast to the

DNA found in single-cell organisms (prokaryotes), eukaryotic genes contain interrupting sequences

that are noncoding. That is, at intervals along a structural gene there are series of bases that do not

participate in the expression of that gene. These are called introns. Exons are those base sequences

that provide the coding of the genes. The introns do base pair when mRNA is transcribed, but the

parts of the message transcribed by these introns are removed by splicing during nuclear RNA

editing prior to export. Each mammalian cell has a complete genome in its nucleus but not all of

this is transcribed. This central molecule of life consists of many discrete sequences which encode

or dictate the amino acid sequence of every protein in the body, which in turn dictates the functional



© 1998 by CRC Press LLC