Non-hemoglobin derived pigment accumulations: melanin, lipofuscin
There are only two non-hemoglobin, endogenous pigment accumulations that are important.
Melanin is an endogenous brown-black pigment produced by melanocytes located in the basal layer of the epidermis, acting as a screen to harmful UV radiation. A number of conditions are the product of increased melanin levels:
- Pigmented nevus
- Fancy name for moles, grow on the skin
- Clusters of melanocytes, can darken after sun exposure
- Addison’s disease
- Aka primary adrenal insufficiency
- Endocrine disorder where the adrenal glands don’t produce enough steroid hormone
- Hyperpigmentation of the skin may be visible, especially in areas not usually exposed to sun (e.g. nipple, buccal mucosa, crease of hand)
- Melanoma
- Cancer that derives from melanocytes
- May develop from pigmented nevus (mole)
- Caused by UV light exposure
On the reverse, some conditions are the product of decreased melanin:
- Albinism
- No tyrosinase enzyme therefore no production of melanin in melanocytes
- Vitiligo
- Local deficiency of melanocytes in the epidermis
Meanwhile Lipofuscin is an insoluble brownish-yellow granular material that accumulates in the heart, liver and brain as well as other tissues. It is composed of lipid and protein complexes that derive from free-radical catalyzed peroxidation of polyunsaturated lipids of subcellular membranes.
H&E, myocardium: lipofuscin as fine yellow-brown granules next to the nuclei of cardiac muscle cells (arrows).
Image: “Myocardial lipofuscin (annotated)” by Mikael Häggström , M.D. Author info - Reusing images - Conflicts of interest: None Mikael Häggström , M.D. Consent note , CC0, via Wikimedia Commons.
This is basically a wear and tear pigment that appears after a cell has been exposed to oxidative stress and the lipids have been oxidised and bound to proteins.
Remember: Lipofuscin is the 'age pigment' – fine yellow-brown granules, often around the nucleus, in long-lived cells (cardiac myocytes, neurons, hepatocytes). It does not harm the cell but marks past free-radical injury. A small, lipofuscin-rich heart of an elderly or cachectic person is called brown atrophy.