Ergosterol, or provitamin D2, is a compound that belongs to the steroid family and is related to cholesterol. It is found in fungi such as Saccharomyces and Candida. This compound is an essential sterol component of fungal and protozoal cell membranes, so it is an important target of antifungal drugs and anti-trypanosomal drugs. In 1927, the relationship of ergosterol and vitamin D was discovered when it was shown that upon exposure to ultraviolet radiation, ergosterol could be used to treat rickets, a disease caused by vitamin D deficiency. It is now known that this compound is a provitamin, or a precursor to vitamin D2 or ergocalciferol.
This compound is structurally similar to cholesterol and when subjected to ultraviolet light, it is turned into vitamin D2. As it is an intrinsic component of fungal cells, it is also found in mushrooms. Other dietary sources include fish liver oil, egg yolk, fortified milk, and other dairy products. Irradiation or exposure of these dietary sources to sunlight results in the conversion of ergosterol into ergocalciferol. Therefore, ergosterol-containing foods and supplements provide a good source of vitamin D, an important nutrient for strong bones and teeth as well as proper calcium balance.
Ergosterol is present in fungi but absent in animals, which is why it serves a big role in the treatment of fungal infections. For instance, amphotericin B, an antifungal drug, binds to ergosterol in order to create pores in the fungal cell membrane. Potassium and other ions and molecules leak through these pores, leading to an imbalance in the internal environment of the fungal cell. This subsequently results in cell death. Amphotericin B, however, has potentially lethal adverse effects, making it a last-line treatment for serious and life-threatening systemic fungal infections.
The azoles, such as clotrimazole, itraconazole, and miconazole, kill fungal cells by inhibiting the enzyme called 14-alpha-demethylase. This enzyme is needed for the production of ergosterol from a precursor compound called lanosterol. Several azole drugs inhibit estrogen production during pregnancy and may cause adverse effects on the fetus.
In its isolated form, provitamin D2 appears as a white or yellow powder that is insoluble in water. This crystalline powder is an irritant to the skin, the mucous membranes of the eyes, and the respiratory tract. Excessive ingestion of this powder can lead to elevated calcium levels in the blood, or hypercalcemia. If left unaddressed, hypercalcemia leads to deposition of calcium salts in different organs of the body.