Thiamin is added to diets as the salt of chloride-hydro-chloride (usually called thiamin hydrochloride) or as the mononitrate. Those forms are stable under dry and acidic conditions, but thiamin is destroyed under alkaline conditions, especially when accompanied by heat. It also is destroyed by X-rays, γ-rays, UV irradiation, and sulfites (Rindi, 1996; Tanphaichitr, 1999).

Thiamin status can be influenced by its bioavailability in food, the presence of antithiamin factors, and dietary concentrations of folate and protein (Tanphaichitr, 1999). Thiaminase I (found in several microorganisms and certain plants, raw fresh-water fish, shellfish, and marine fish) and thiaminase II (found in several microorganisms) are thermolabile antithiamin factors that destroy the vitamin activity of thiamin during food storage or preparation, prior to ingestion or during food passage through the gastrointestinal tract. Thermostable antithiamin factors have been found in plants and a few animal tissues. Those in plants are related to ortho- and para-polyphenolic compounds, such as caffeic acid, chlorogenic acid, and tannic acid. In the presence of oxygen, active quinones are generated that interact with thiamin to produce thiamin disulfide and other less active or inactive compounds. Ascorbic acid and other reducing agents tend to inhibit this process. The bioavailability of thiamin in foods also may be reduced by divalent cations, such as Ca2+ and Mg2+, which tend to augment the precipitation of thiamin by tannins. Ascorbic acid, tartaric acid, and citric acid will inhibit this precipitation, apparently by sequestering these cations. Subjects with a folate or protein deficiency exhibit a reduction in thiamin absorption that can be reversed by folate and protein supplementation.

Thiamin deficiency has been produced in rhesus monkeys (Macaca mulatta) by Lebond and Chaulin-Serviniere (1942), Waisman and McCall (1944), Rinehart et al. (1948,1949a), Blank et al. (1975), Witt and Goldman-Rakic (1983a), and Cogan et al. (1985). Deficiency signs include weight loss, anorexia, apathy, weakness, ophthalmoplegia, loss of reflexes, paralysis, incoordination, convulsions, cardiac failure, and death. Thiamin-deficient animals also exhibit behavioral abnormalities and memory loss (Witt and Goldman-Rakic, 1983b).

Observations of pathologic conditions have focused on the myocardium and the nervous system. Focal necrosis of myocardial fibers is a relatively constant finding and has been associated with electrocardiographic abnormalities. Degeneration of the fibers in the myocardial conduction system also has been seen (Waisman and McCall, 1944; Rinehart and Greenberg, 1949a). Both peripheral nerve (Lebond and Chaulin-Serviniere, 1942) and central nervous system degeneration similar to Wernick’s encephalopathy (Rinehart et al., 1949; Blank et al., 1975; Witt and Goldman-Rakic, 1983a, 1983b) have been described in rhesus monkeys. Wernick’s encephalopathy is a disease often associated with chronic alcoholism in humans.

Waisman and McCall (1944) found that rhesus monkeys weighing about 3 kg and consuming 100-200 g of food per day required thiamin at 15 μg·BWkg−1·d−1 to prevent deficiency signs and support maintenance. Optimal growth was obtained at 25-30 μg·BWkg−1·d−1, whereas borderline deficiency signs appeared in animals receiving less than 10 μg·BWkg−1·d−1.

Rinehart et al. (1948) described an anemia associated with reduced erythropoiesis in thiamin deficiency. They estimated the thiamin requirement by observing the time necessary to replete thiamin-deficient rhesus monkeys weighing 1.7-5.0 kg after administration of a single small thiamin dose separate from food. The researchers concluded that the thiamin requirement was about 15.5 μg·BWkg−1·d−1.

Thiamin-deficient rhesus monkeys have reduced blood transketolase activity (Mesulam et al., 1977), an accepted end point for assessing thiamin status (Rindi, 1996). However, measurements of transketolase activity have not been applied to studies of the quantitative thiamin requirement.

The quantitative requirement for thiamin has not been studied in nonhuman primates other than rhesus monkeys. However, the thiamin requirement of nonhuman primates is estimated to be 1.1 mg·kg−1 of dietary DM, primarily on the basis of the report of Waisman and McCall (1944). That estimate was based on the use of purified diets, and the biologic availability of thiamin in natural ingredients and the destruction of thiamin during feed processing or storage were not taken into account. These studies are summarized in Table 7-2.

Riboflavin

Riboflavin is a precursor of the coenzymes flavine adenine mononucleotide (FMN) and flavine adenine dinucleotide (FAD). Those coenzymes and their associated enzymes catalyze oxidation-reduction reactions and are important in the metabolism of carbohydrates, fats, and proteins. The enzymes function in the transfer of electrons in oxidation-reduction reactions (Rivlin, 1996). A riboflavin coenzyme also plays a role in the conversion of pyridoxine to pyridoxamine phosphate, which acts as a coenzyme in the conversion of tryptophan to niacin. Thus, riboflavin may be involved indirectly in the biosynthesis of niacin from tryptophan (Cooperman and Lopez, 1991; McCormack, 1999).

Riboflavin is added to animal feeds in the form of the crystalline vitamin. The biologic availability to humans of riboflavin in natural foods is estimated to be about 95% (Institute of Medicine, 1998).

Riboflavin deficiency has been induced and studied in rhesus monkeys (Macaca mulatta) by Day et al. (1935),



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