aminolevulinic acid
Meaning of aminolevulinic acid: A colorless building block that tumor cells convert into a red-glowing pigment, used both to reveal tissue and to destroy it.
Definition of aminolevulinic acid
Aminolevulinic acid is a small naturally occurring molecule, the first building block the body uses to construct heme, the red pigment that carries oxygen in blood. Supplied from outside in excess, it is taken up by cells and converted into protoporphyrin, a compound that glows red under blue light and, once lit, produces enough reactive oxygen to kill the cell holding it.
Why does it build up in tumors?
The final step of heme production slots an iron atom into protoporphyrin, and that step is the bottleneck. Flooding cells with the starting material outruns it, so the glowing intermediate piles up before iron can be added. Cancer cells tend to accumulate more and clear it more slowly than the tissue around them, giving a contrast that lasts several hours. The compound given is inactive in itself, which is the detail most often left out: it is a precursor, and the pigment the cell manufactures from it is what absorbs light and does the work. Chemically it is an amino acid, though not one of those used to build proteins.
What is it used for?
| Use | How it is given | What the light does |
|---|---|---|
| Actinic keratosis of the skin | Applied to the area, then illuminated | Destroys the abnormal cells |
| Surgery for high-grade brain tumor | Drunk before the operation | Makes tumor glow so its edge can be seen |
| Inspection of the bladder lining | Instilled as a related compound | Marks flat tumor that white light misses |
The first of these treats actinic keratosis, rough sun-damaged patches that can progress to skin cancer. The second is not treatment at all but vision: under blue-violet light the tumor fluoresces pink while normal brain stays dark, so more of the growth can be identified during removal.
What does the light actually do?
The pigment absorbs a photon and hands the energy to nearby oxygen, creating a highly reactive form of it that survives for a fraction of a microsecond. In that instant it tears into whatever membrane or protein sits alongside, so damage never travels beyond the cell that made the pigment. Killing therefore requires three things to coincide: the compound, oxygen, and light of the right color reaching the spot. That is why the treatment is confined to surfaces and to places a light source can be delivered. Because it works as a photosensitizing agent, skin and eyes stay unusually sensitive to bright light for a day or so after a dose.
Also known as
Used in a sentence
Aminolevulinic acid was given before surgery to allow fluorescence guidance.
Good to know
The compound given is inactive; the cell converts it into protoporphyrin, and that pigment absorbs the light and generates the reactive oxygen, so the effect is limited to illuminated tissue that has accumulated pigment.