Vitamin A (Retinoids) Lecture Notes

Introduction

• Presenter: Medicosis Perfectionalis
• Topic: Vitamin A (Retinoids)
• Forms of Vitamin A:
  • Retinol
  • Retinal
  • Retinoic Acid
• Importance:
  • Essential for eyes and epithelium

Understanding Skin Tone

• Three substances determining skin tone:
  • Melanin (most influential)
  • Beta-carotene
  • Hemoglobin
• Conditions related to melanin:
  • Hyperpigmentation (too much melanin)
  • Albinism (too little melanin)
  • Hypercarotinemia (excess beta-carotene)
  • Anemia (low hemoglobin leads to pale skin)
  • Metahemoglobinemia (causes cyanotic skin)

Vitamin A Deficiency

• Historical context: Ancient Egyptians used liver to treat vision issues
• Common symptoms:
  • Night blindness (nyctalopia)
  • Dry eyes (xerophthalmia)
  • Keratomalacia (corneal ulcers)
  • Skin conditions like phryoderma
  • Bone and teeth problems
  • Iron deficiency anemia
• Causes:
  • Dietary deficiency
  • Issues with absorption (malabsorption)
  • Liver problems

Biochemistry of Vitamin A

• Types:
  • Retinol (alcohol)
  • Retinal (aldehyde)
  • Retinoic Acid (carboxylic acid)
• Pro-vitamins: Carotenes (alpha, beta, gamma)
• Sources:
  • Natural: liver oil, egg yolk, butter, milk, carrots, green and yellow vegetables
  • Artificial: supplements
• Daily Requirement: ~3000 IU/day
• Blood levels: 18 to 60 mcg/dL

Functions of Vitamin A

• Vision (especially night vision)
• Cell division and growth
• Bone and teeth health
• Epithelialization and metabolism
• Immune system support
• Reproductive health (notably in males)

Metabolism and Absorption

• Fat soluble, requiring:
  • Pancreatic enzymes (lipase, colipase)
  • Bile salts
• Process:
  • Consumed as vitamin A ester
  • Broken down by cholesterol esterase to retinol
  • Absorbed and re-esterified in the gut
  • Stored in the liver as retinol ester
• Transported via proteins (RBP, RABP)

Vitamin A Deficiency Effects

• Clinical Symptoms:
  • Night blindness
  • Dry skin and eyes
  • Follicular hyperkeratosis
  • Decreased immunity
• Causes:
  • Malabsorption syndromes
  • Liver or pancreatic issues
  • Dietary deficiency

Hypervitaminosis A

• Acute Symptoms:
  • Blurred vision, headache, nausea
• Chronic Symptoms:
  • Weight loss, anorexia, bone fractures
• Case Example: Polar bear liver consumption

Therapeutic Uses

• Treats:
  • Vitamin A deficiency
  • Acne (topical for mild, oral for severe)
  • Acute promyelocytic leukemia (APL)
  • Measles
• Precaution: Teratogenic effect

Pharmacological Aspects

• Drug Interactions:
  • Fumepizole inhibits alcohol dehydrogenase
  • Disulfiram inhibits acetaldehyde dehydrogenase
• Zinc: Important for alcohol and aldehyde dehydrogenases
• Related Conditions:
  • Acrodermatitis enteropathica (zinc deficiency)

Conclusion

• Vitamin A plays a crucial role in vision, epithelial health, and immune function.
• Both deficiency and excess of vitamin A present significant health issues.
• Ensuring adequate intake and absorption is vital for health.

Additional Resources

• Visit medicosisperfectionist.com for more courses and resources.