ABSTRACT
Biotin deficiency is characterized by anorexia, nausea, vomiting, glossitis, pallor, mental depression, hair loss (alopecia), dry scaly dermatitis, and an increase in serum cholesterol and bile pigments.5 Human deficiency is rare but can occur through prolonged consumption of raw egg and parenteral feeding without biotin supplementation in patients with short-gut syndrome.5,15 Biotin deficiency occurs in infants through an inborn error of metabolism that leads to lack of biotinidase, the enzyme necessary to cleave biotinyl-lysine bonds in biocytin (biotinyl-ε-lysine). Mock5 indicates that the lack of biotinidase produces biotin deficiency by leading to inefficient release of protein-bound biotin in the gastrointestinal tract, less salvage of biotin at the cellular level, and through increased renal loss. Biotin deficiency has been linked to sudden infant death syndrome; however, firm conclusions have not been made in this significant area. Biotinidase deficiency results in a secondary biotin deficiency owing to inefficient biotin absorption in the gut, less salvage of biotin at the cellular level, and increased renal loss of biotin and biocytin.6 Profound biotinidase deficiency is defined by a less than 10% level of normal serum activity. Symptoms of biotinidase deficiency include seizures, hypotonia, skin rash, alopecia, developmental delay, conjunctivitis, visual problems, hearing problems, mental retardation, keetolactic acidosis, and organic aciduria.7−9 More accurate assay techniques primarily using liquid chromatography (LC) linked to avidin-binding assays have provided better status indicators. Measurement of urinary excretion and excretion of biotin metabolites are, now, good indicators of biotin status.6,10−12 Decreased urinary excretion of biotin and bisnorbiotin are early and sensitive indicators of biotin deficiency while serum concentration change is not.10,11 Urinary excretion of 3-hydroxyisovaleric acid, a leucine metabolite, increases owing to the lack of β-methylcrotonyl-CoA carboxylase due to biotin deficiency. Increased urinary excretion of this metabolite is considered to be a good indicator of biotin deficiency.6,11 Assessing
marginal biotin deficiency is of particular concern during pregnancy since the deficiency is teratogenic in some animal species.12−14
Biotin occurs in relatively low concentrations in most foods. Liver and yeast are high in biotin content compared to other foods. Substantial sources are egg yolk, dairy products, soy products, cereals, and vegetables. Meat and fruit are low in biotin.15 Data on the biotin content of food is not published in most food composition databases.15 Relatively few studies have been published with few foods analyzed.16−24 More recent development of sensitive and specific LC/avidin binding assays offer improved analytical values for food.24 Staggs et al.24 used LC coupled to an off-line avidin binding assay that distinguishes biotin from inactive metabolites to assay total biotin content of 87 foods. Comparison of the values to previously published values showed that the values obtained with the LC/avidin binding methods disagreed substantially with previously published values for like foods. Values varied from 247 times greater than published to as much as 36% less. Among 51 foods assayed for which published values were available, only seven agreed within ±20%. The authors concluded that most published values for biotin are likely inaccurate. Data from the Staggs et al.24 study are provided in Table 12.1. Much of the previously published data was obtained by microbiological assay with Lactobacillus plantarum ATCC 8014. Biotin is present in food in the free form and covalently bound to polypeptides through a lysine residue.6 Proteases degrade the protein-bound biotin to biocytin (biotinyl-ε-lysine), which is broken down to liberate free biotin by biotinidase, which facilitates absorption. Microbial synthesis in the gut is a source of biotin; however, the significance of microbial synthesis to total biotin available to the human is unknown. The role of avidin as a biotin antagonist is understood. Nutritionally, the binding phenomenon has little impact since cooking destroys the avidinbiotin complex and denatures avidin, preventing additional complex formation. Raw egg white, if added to foods without further cooking or ingested with cooked foods, provides avidin that binds the low amounts of biotin in the food. The avidin-biotin complex resists digestive proteases and prevents absorption.
