Melanin

Melanin is a natural pigment found in most organisms, responsible for the color of skin, hair, and eyes. It also plays a crucial role in protecting the skin from ultraviolet (UV) radiation damage by absorbing and dissipating harmful rays.

Types of Melanin

There are three main types of melanin:

1. Eumelanin – Found in black and brown pigments in hair, skin, and eyes.
2. Pheomelanin – Produces red and yellow hues, mainly found in lips, red hair, and freckles.
3. Neuromelanin – Present in the brain, where it may play a role in protecting neurons.

Melanin Synthesis (Melanogenesis)

Melanin is synthesized in specialized cells called melanocytes, which are found in the basal layer of the epidermis. The synthesis occurs in organelles within melanocytes called melanosomes and follows these key steps:

1. Initiation by Tyrosinase:

   • The amino acid tyrosine is converted into L-DOPA (L-3,4-dihydroxyphenylalanine) by the enzyme tyrosinase.
   • L-DOPA is further oxidized into dopaquinone.

2. Pathway Divergence:

   • Dopaquinone can follow different pathways to form eumelanin or pheomelanin, depending on the availability of cysteine and other biochemical conditions.
   • If cysteine is present, dopaquinone is converted into cysteinyldopa, leading to pheomelanin synthesis.
   • If cysteine is absent, dopaquinone undergoes further oxidation and polymerization, forming eumelanin.

3. Melanin Transport & Deposition:

   • Melanosomes containing melanin are transported via dendritic processes from melanocytes to keratinocytes, the primary cells of the epidermis.
   • In keratinocytes, melanin acts as a protective shield over the nucleus to absorb UV radiation and reduce DNA damage.

Regulation of Melanin Production

Melanin synthesis is influenced by various factors:

• Genetics: Determines baseline melanin levels and type (e.g., darker skin tones have more eumelanin).
• UV Exposure: Stimulates tyrosinase activity, leading to increased melanin production (tanning).
• Hormones: Melanocyte-stimulating hormone (MSH) enhances melanin synthesis.
• Inflammation & Injury: Can cause post-inflammatory hyperpigmentation (e.g., dark spots after acne).
• Nutritional Factors: Copper and vitamin C are essential for melanin synthesis, as tyrosinase is a copper-dependent enzyme.

Disorders Related to Melanin Synthesis

• Albinism: A genetic disorder resulting from mutations in tyrosinase or other enzymes, leading to little or no melanin production.
• Vitiligo: An autoimmune condition where melanocytes are destroyed, causing depigmented patches on the skin.
• Melasma: Overproduction of melanin, often triggered by hormonal changes or sun exposure, causing dark patches on the skin.
• Parkinson’s Disease: Loss of neuromelanin-producing neurons in the brain is linked to this neurodegenerative disorder.