Desmosterol is an immediate precursor of cholesterol in the Bloch pathway of sterol synthesis and an abundant membrane lipid in specific cell types. Desmosterol has become of particular interest in the pathogenesis of Alzheimer's disease (AD) because of the report that the activity of the gene coding for the enzyme Δ24-dehydrocholesterol reductase (DHCR24), which metabolizes desmosterol to cholesterol, is selectively reduced in the affected areas of the brain. Any change in the pattern of C27 sterol intermediates in cholesterol synthesis merits investigation with respect to the pathogenesis of AD, since neurosteroids such as progesterone can modulate the tissue levels. The significant elevation of plasma desmosterol levels was revealed in patients with desmosterolosis, a rare disorder of cholesterol biosynthesis, which is caused by mutations in DHCR24. In addition, was shown, that desmosterol can be oxidized by Cytochrome P450 46A1, which is expressed in brain and as a consequence, the formation of that oxysterols in the brain could be related to the Smith-Lemli-Opitz syndrome, desmosterolosis, and other relevant diseases, as well as with signal transduction by lipids.

3.beta-3-[2-(Diethylamino)ethoxy]androst-5-en-17-one hydrochloride or U18666A, an amphipathic cationic amine, is a cell permeable research tool drug that inhibits cholesterol synthesis and trafficking, and also a weak inhibitor of hedgehog (Hh) signaling. U18666A had been used in several models both in vivo and in vitro to mimic Niemann-Pick type C disease (NPC) and for assessing the importance of molecular trafficking through the lysosomal pathway in other conditions such as atherosclerosis, Alzheimer's disease, and prion infections. U18666A also provided animal models for such disorders as petite mal (absence) epilepsy and cataracts. U18666A inhibits the enzyme desmosterol reductase responsible for reducing the desmosterol in cholesterol biosynthesis, and also blocks LDL-(low density lipoprotein) cholesterol transport from the lysosomes into the endoplasmic reticulum thereby increasing the level of caveolina-1 located within the plasma membrane caveolae. U18666A was shown to be a potent antagonist of alpha4beta2 neuronal nicotinic acetylcholine receptors and may be useful as a tool in the functional characterization and pharmacological profiling of nAChRs.

Triparanol (brand and developmental code names MER/29) is a 24-dehydro cholesterol reductase inhibitor, which is an enzyme involved in the biosynthesis of cholesterol. It has antitumor properties, such as decreasing proliferation and inducing apoptosis in many cancer cell lines and slowing tumor growth in a mouse xenograft model. It can also decrease Hedgehog pathway signaling in cancer cells. Triparanol was the first synthetic cholesterol-lowering drug. It was withdrawn in 1962 due to severe adverse effects such as nausea and vomiting, vision loss due to irreversible cataracts, alopecia, skin disorders (e.g., dryness, itching, peeling, and "fish-scale" texture), and accelerated atherosclerosis and is now considered to be obsolete.

3.beta-3-[2-(Diethylamino)ethoxy]androst-5-en-17-one hydrochloride or U18666A, an amphipathic cationic amine, is a cell permeable research tool drug that inhibits cholesterol synthesis and trafficking, and also a weak inhibitor of hedgehog (Hh) signaling. U18666A had been used in several models both in vivo and in vitro to mimic Niemann-Pick type C disease (NPC) and for assessing the importance of molecular trafficking through the lysosomal pathway in other conditions such as atherosclerosis, Alzheimer's disease, and prion infections. U18666A also provided animal models for such disorders as petite mal (absence) epilepsy and cataracts. U18666A inhibits the enzyme desmosterol reductase responsible for reducing the desmosterol in cholesterol biosynthesis, and also blocks LDL-(low density lipoprotein) cholesterol transport from the lysosomes into the endoplasmic reticulum thereby increasing the level of caveolina-1 located within the plasma membrane caveolae. U18666A was shown to be a potent antagonist of alpha4beta2 neuronal nicotinic acetylcholine receptors and may be useful as a tool in the functional characterization and pharmacological profiling of nAChRs.