Biotin-B7- Metabolism, utilization transport.pptx

Biotin -B7 Vitamin, Its food sources, metabolism storage, excretion and deficiency symptoms observed in humans

1. Biotin-B7 Metabolism, transport, storage, Utilization, sources and deficiency

2. Biotin, also known as vitamin B7 or vitamin H, is a water-soluble B vitamin that plays a critical role in various metabolic processes in the human body. It is essential for the metabolism of carbohydrates, fats, and proteins .

3. 1. Absorption and Transport Biotin is absorbed in the small intestine. The main sources of biotin include dietary intake from foods like eggs, nuts, seeds, and certain vegetables, as well as endogenous production by gut microbiota . Dietary Biotin: In foods, biotin is often found bound to proteins. During digestion, proteolytic enzymes release free biotin, which is then absorbed in the small intestine, primarily in the jejunum and ileum. Biotin from Gut Microbiota : The gut microbiota can synthesize biotin, which can also be absorbed in the colon, although this contribution is generally minor compared to dietary sources. Biotin is absorbed via a sodium-dependent multivitamin transporter (SMVT). Once absorbed, it is transported through the bloodstream bound to plasma proteins.

4. 2 . Cellular Uptake and Activation Within cells, biotin functions as a coenzyme for carboxylase enzymes. It is attached to carboxylase enzymes through a process called biotinylation , facilitated by holocarboxylase synthetase . The biotinylated enzymes are essential for several metabolic pathways: Acetyl- CoA Carboxylase (ACC): Involved in fatty acid synthesis. Pyruvate Carboxylase (PC): Critical in gluconeogenesis , converting pyruvate to oxaloacetate . Propionyl-CoA Carboxylase (PCC): Involved in the metabolism of certain amino acids and odd-chain fatty acids. 3-Methylcrotonyl-CoA Carboxylase (MCC): Involved in the metabolism of the amino acid leucine .

5. Biotin Recycling and Degradation The body efficiently recycles biotin through the action of biotinidase , an enzyme that releases biotin from biotinylated proteins and peptides. This free biotin can then be reused or excreted. Biotin that is not reused or recycled can be degraded. Biotin degradation involves the cleavage of the valeric acid side chain, resulting in products that are excreted in urine.

6. D ietary sources of biotin: Animal-Based Sources Eggs : Particularly the yolk, which is a concentrated source of biotin. However, raw egg whites contain avidin , a protein that can bind to biotin and prevent its absorption. Liver and Organ Meats : Chicken liver, beef liver, and other organ meats are excellent sources of biotin. Fish : Some fish, such as salmon, are good sources of biotin. Meat : Other meats, such as pork and beef, also contain biotin. Dairy Products : Milk, cheese, and yogurt provide moderate amounts of biotin.

7. Plant-Based Sources Nuts and Seeds : Almonds, walnuts, peanuts, sunflower seeds, and other nuts and seeds are good sources. Legumes : Peanuts, soybeans, and other legumes contain biotin. Whole Grains : Foods like oats, barley, and wheat contain biotin, though the levels can vary depending on processing. Vegetables : Some vegetables, including sweet potatoes, spinach, broccoli, and cauliflower, provide biotin. Fruits : Certain fruits, such as bananas and avocados, contain smaller amounts of biotin.

8. Fortified Foods Many foods, including breakfast cereals, are fortified with biotin, providing an additional source of this vitamin. Biotin from Gut Microbiota While not a dietary source per se, the bacteria in the human gut can synthesize biotin. However, the contribution of this source to overall biotin status is considered to be minimal compared to dietary intake. Considerations for Biotin Absorption Cooking and Processing : Cooking and food processing can reduce the biotin content of foods. However, this is generally not a significant concern for most people with a balanced diet. Raw Egg Whites : Consuming raw egg whites should be avoided, as they contain avidin , which binds biotin and can lead to deficiency if consumed in large quantities over time.

9. Utilisation of Biotin 1. As a Coenzyme in Metabolism Biotin functions as a coenzyme for several carboxylase enzymes, which are critical in the metabolism of carbohydrates, fats, and proteins: Acetyl- CoA Carboxylase (ACC) : This enzyme is involved in the synthesis of fatty acids. It catalyzes the conversion of acetyl- CoA to malonyl-CoA , a key step in fatty acid biosynthesis. Pyruvate Carboxylase (PC) : This enzyme is crucial for gluconeogenesis , the metabolic pathway that generates glucose from non-carbohydrate sources. It catalyzes the conversion of pyruvate to oxaloacetate . Propionyl-CoA Carboxylase (PCC) : PCC is involved in the metabolism of certain amino acids ( valine , isoleucine , methionine , and threonine ) and odd-chain fatty acids, converting propionyl-CoA to methylmalonyl-CoA . 3-Methylcrotonyl-CoA Carboxylase (MCC) : This enzyme is involved in the breakdown of the amino acid leucine , converting 3-methylcrotonyl-CoA to 3-methylglutaconyl-CoA.

10. 2. Gene Expression Regulation Biotin plays a role in the regulation of gene expression. It is involved in the biotinylation of histones , which are proteins associated with DNA in the nucleus. This modification can influence the structure of chromatin and thereby affect gene expression. Biotin's role in gene regulation is essential for processes like cell signaling, DNA repair, and cell proliferation.

11. 3 . Supporting Healthy Skin, Hair, and Nails Biotin is often associated with healthy skin, hair, and nails. biotin is thought to contribute to the production of keratin, a protein that is a key structural component of hair, skin, and nails. Biotin deficiency can lead to symptoms like hair thinning, brittle nails, and skin rashes.

12. 4. Energy Production and Metabolism Through its role in the activity of carboxylase enzymes, biotin is crucial in the production of energy from nutrients. It helps convert carbohydrates, fats, and proteins into energy, which is essential for maintaining normal metabolic processes.

13. 5. Nervous System Function Biotin is important for nervous system health. It helps in the synthesis of neurotransmitters and supports myelin formation, a fatty layer that surrounds and protects nerve fibers. Biotin deficiency can lead to neurological symptoms such as depression, lethargy, and hallucinations.

14. Causes of Biotin Deficiency Dietary Deficiency: Inadequate Intake: Although biotin is found in various foods, a diet severely lacking in biotin-rich foods can lead to deficiency. Raw Egg Consumption: Consuming large amounts of raw egg whites can cause deficiency. Raw egg whites contain avidin , a protein that binds

15. Genetic Disorders: Biotinidase Deficiency: This rare genetic disorder reduces the ability to recycle biotin from biocytin and dietary proteins, leading to biotin deficiency. It can cause severe neurological and dermatological symptoms if untreated. Holocarboxylase Synthetase Deficiency: Another genetic condition affecting biotin utilization, it impairs the body's ability to attach biotin to carboxylase enzymes, crucial for metabolic functions.

16. Impaired Absorption: Gastrointestinal Disorders: Conditions like inflammatory bowel disease (IBD), celiac disease, and other malabsorption syndromes can reduce the absorption of biotin. Long-term Use of Antibiotics: Prolonged antibiotic use can alter gut microbiota , reducing biotin production by intestinal bacteria.

17. Increased Biotin Requirements: Pregnancy and Lactation: Increased demand for biotin can occur during pregnancy and lactation, potentially leading to deficiency if intake is insufficient. Medications: Certain medications , like anticonvulsants (e.g., valproic acid, carbamazepine ), can reduce biotin levels by increasing its metabolism or interfering with absorption.

18. Storage of Biotin In Human 1. Storage in the Body Limited Storage: Biotin is stored in small amounts in the liver and possibly other tissues, but these stores are limited. As a result, a continuous intake of biotin is necessary to maintain adequate levels. Turnover and Excretion: The body efficiently recycles biotin through the action of the enzyme biotinidase , which releases biotin from biotinylated proteins and peptides. Excess biotin not used by the body is excreted in urine, minimizing the risk of toxicity.

19. 2. Dietary Intake and Absorption Regular Intake Needed: Because biotin is not stored in large quantities, regular dietary intake is essential to prevent deficiency. Biotin-rich foods include eggs (cooked), liver, nuts, seeds, and certain vegetables. Bioavailability: The bioavailability of biotin can be affected by factors such as the presence of avidin in raw egg whites, which can bind to biotin and inhibit its absorption. Cooking egg whites denatures avidin , preventing this binding.

20. 3. Storage of Biotin Supplements Proper Storage Conditions: Biotin supplements, like other vitamins, should be stored in a cool, dry place away from direct sunlight and moisture. The ideal storage temperature is typically room temperature, between 15-30°C (59-86°F). Container: Biotin supplements should be kept in their original, tightly sealed containers to protect them from environmental factors that could degrade their potency. Shelf Life: Biotin supplements generally have a long shelf life when stored properly, but it's important to check the expiration date and use them within the recommended time frame to ensure effectiveness.

21. 4. Handling of Biotin-Rich Foods Food Preparation: Cooking and food processing can reduce the biotin content of foods. To preserve biotin, it's best to cook foods gently and avoid excessive processing. However, some cooking methods, like boiling, can cause biotin to leach into the cooking water. Avoid Raw Egg Whites: As mentioned, consuming raw egg whites should be avoided due to the presence of avidin , which binds biotin and prevents its absorption. Cooking egg whites denatures avidin , making the biotin in the yolk more bioavailable .

22. Symptoms of Biotin Deficiency Dermatological Symptoms: Hair loss (alopecia) Red, scaly rash, particularly around the eyes, nose, mouth, and genital area Dry or cracking skin Neurological Symptoms: Depression Lethargy and fatigue Hallucinations Paresthesia (tingling or numbness in the limbs) Muscle pain and weakness Developmental delays and seizures (in infants) Other Symptoms: Conjunctivitis (eye inflammation) Glossitis (swollen tongue) Loss of appetite and nausea

23. Treatment of Biotin Deficiency Biotin Supplementation: Oral biotin supplements can effectively treat deficiency. The dosage depends on the severity of the deficiency and the underlying cause. In cases of genetic disorders, higher doses may be necessary. Dietary Modifications: Increasing the intake of biotin-rich foods, such as eggs (cooked), liver, nuts, seeds, and vegetables, can help prevent and manage deficiency. Managing Underlying Conditions: Treating gastrointestinal disorders or adjusting medications that interfere with biotin absorption or metabolism may be necessary. Prenatal Care: Pregnant and lactating women may need to ensure adequate biotin intake, either through diet or supplements, to meet increased nutritional demands.

24. Roles of the 5 biotin-dependent carboxylases of CoA and ACP within the cell. Shown is an overview of the metabolic pathways of ACC1 ( cytosolic ) and ACC2 (outer mitochondrial membrane) and the 3 mitochondrial carboxylases PCC, MCC, and PC. ACC1, acetyl- CoA carboxylase 1; ACC2, acetyl- CoA carboxylase 2; ACP, acyl carrier protein; HMG, 3-hydroxy-3-methylglutaryl; MCC, methylcrotonyl-CoA carboxylase ; PC, pyruvate carboxylase ; PCC, propionyl-CoA carboxylase ; PDH, pyruvate dehydrogenase . 

25. The biotin cycle and the HCS-dependent transcriptional regulation in human cells. Shown is a schematic representation of the biotin cycle ( green arrows ) and the HCS-dependent signal transduction pathway ( red arrows ) responsible for the transcriptional regulation of PC, PCC, MCC, ACC, sodium-dependent multivitamin transporter ( SMVT ), and HCS. The enzymes participating in the HCS pathway are sGC and PKG. 

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