Lumisterol, more specifically lumisterol2 (L2), is a compound that is part of the vitamin D family of steroid compounds. It is the (9β,10α) stereoisomer of ergosterol and occurs as a photochemical by-product in the preparation of vitamin D1, a mixture of vitamin D2 and lumisterol. Lumisterol has an analog based on 7-dehydrocholesterol, known as lumisterol 3 or lumisterol3 (L3).
Formation Lumisterol is produced when previtamin D, instead of isomerizing to vitamin D, receives an additional UVB photon to cause a disrotatory electrocyclic ring-closure. In vivo this happens under high-dose or prolonged UVB exposure.
Reactions Vitamin D2 can be formed from L2 by an electrocyclic ring opening (back to the previtamin) and subsequent sigmatropic [1,7] hydride shift. This conversion reaction can be stimulated by UV-B or heat. At very high doses in mice, this conversion can occur in the body.
L2 is metabolized by CYP27A1, causing hydroxylation at the 24, 27, 28 positions.
L3 is processed by CYP27A1 to form products hydroxylated at positions 25 and/or 27. CYP11A1 can 20S-hydroxylate L3. The resulting products are biologically active. Many of these products activate UV-defense mechanisms in keratinocytes.
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