Biotin - Vitamin B7

Vitamin B7

Biotin

Sources

* liver, eggs (higher amounts)
* meats, canned salmon, sunflower seeds, sweet potatoes (smaller amounts)

In raw eggs whites what binds to biotin & makes the tightest non-covalent bond found in nature?

avidin

What does the binding of avidin and biotin prevent?

prevents of the absorption of biotin

What is biocytin made of?

Biotin bound to the AA lysine

What does biotinidase deficiency results from?

an autosomal recessive inborn error of metabolism

Biotinidase deficiency

* impairs digestion of lysine-bound biotin
* hamper biotin release & recycles biotin in tissues

Manifestations of the biotinidase deficiency

* lethargy, hypotonia (reduced muscle tone), seizures, ataxia (impaired muscle control)
* detmatitis and alopecia

Where does biotin absorption occur?

mainly in the proximal small intestine; but also in the proximal and midtransverse colon

Where is biotin stored in the body?

muscle, liver and brain

Noncoenzyme Roles of Biotin

* functions in the modification of histone proteins
* in gene expression and cell signaling

Pharmacological Uses of Biotin:

* mainly in the management of a handful of inborn errors of metabolism that involve biotin dependent enzymes
* oral supplements in amounts of 5-20 mg daily are used to treat biotinidase deficiency

Where is biotin excreted?

in the feces - very small amounts

Where are biotin metabolites excreted from in the body?

Via the urine

AI of biotin

* Adults: 30 ug/day
* Pregnant or lactating: 30-35 ug/day

Biotin deficiency

* rare
* can result from excessive consumption of raw egg whites

Manifestations of biotin deficiency

* Neurological symptoms: lethargy, paresthesia in extremities, hypertonia, depression, and hallucinations
* red, dry, scaly dermatitis found around the eyes, nose, mouth, and perineum
* anorexia, nausea, alopecia, brittle nails, and muscle pain may occur
* death may occur is untreated

At risk for deficiency:

* people who ingest raw eggs in excess because avidin’s binding to the biotin prevents the vitamin’s absoprtion
* impaired absorption may also occur in GI disorders such as IBD
* consumes excessive alcohol
* decline in some women during pregnancy with lactation

Toxicity

* no toxicity from oral ingestion has been reported