Cholesterol

Cholesterol is a sterol compound that is an important component of animal plasma membranes and other organelles. It regulates membrane integrity, fluidity and permeability. Additionally, cholesterol is a precursor to steroid hormones, bile acids, and vitamin D. New research finds that cholesterol also plays an important role in cell signaling and lipid absorption. In addition, cholesterol is also widely used in the field of pharmaceutical research, such as in the preparation of lipid nanoparticles to deliver mRNA, DNA, peptides, proteins, etc. Cholesterol is a hydrophobic molecule with very low water solubility. Cholesterol PEG with carboxylic acid functionality can be activated to react with amines or hydroxyl groups. Cholesterol PEG derivatives have been successfully used in cell membrane imaging, liposome formulation and drug delivery. In addition, PEG cholesterol derivatives can be used to make liposomes to shorten the cycle time of encapsulated drugs, and they can also be used in non-viral transfection reagents.

BOC Sciences provides high-purity cholesterol compounds suitable for a wide range of pharmaceutical research and industrial production. The cholesterol compounds we offer are rigorously tested for quality and purity to ensure consistent experimental results. Researchers and pharmaceutical companies can rely on BOC Sciences to provide a reliable supply of cholesterol for their research and product development. If you are interested in our lipid or cholesterol compounds, please contact us for more information.

Biosynthesis of Cholesterol

The structure of cholesterol can be divided into four parts: A-D. As shown in Fig 1, the A part is the polar group C3-OH, which can form hydrogen bonds with the enzyme and is the polar head part of the whole molecule; the B part is a ring region composed of 6-6-6-5 rings, in which the C4 methyl will affect the conformation of the A ring. In addition, the number and position of the double bond of the molecule will affect the shape of the sterol and the inclination of the C17 (C20) bond; the C part contains only one chiral atom C20, and its chirality has been confirmed as the R configuration in previous studies, which also determines the direction of the aliphatic side chain as the 'right hand' orientation; in the D part, the conformation and length of the aliphatic side chain, as well as the stereochemistry of the C24-alkyl group in phytosterols, are crucial for intermolecular contact.

Fig. 1. Perspective view of a cholesterol molecule (Chem Rev. 2011, 111(10): 6423-6451).

The cholesterol molecule has 8 chiral atoms and theoretically has 2⁸ (256) different stereoisomers, but in fact there is only one endogenously synthesized cholesterol molecule. This illustrates the importance of stereospecific control of enzymes during cholesterol synthesis. The entire cholesterol synthesis is divided into two parts. The first part is the formation from acetyl CoA to lanosterol, and the second part is the synthesis process from lanosterol to cholesterol. Acetyl CoA is the raw material for synthesizing cholesterol. Two molecules of acetyl CoA synthesize one molecule of acetyl CoA-mevalonate; acetyl CoA-mevalonate then generates the basic units of terpenes IPP and DMAPP through the MVA pathway, and then passes through isoprene. The rules extend from C5 to C30 squalene (squalene). Squalene is oxidized to form squalene oxide, which is then cyclized and rearranged to form the cholesterol precursor compound lanosterol, and then undergoes a series of modifications to obtain cholesterol.

Table 1. The basics of cholesterol synthesis

Cholesterol in Drug Discovery

Cholesterol has become a versatile tool in drug delivery and drug development. Cholesterol's unique physicochemical properties, such as its amphipathic nature and ability to interact with lipids and proteins, make it an attractive candidate for improved delivery of therapeutic agents.

Cholesterol in Drug Delivery

The ability of cholesterol to modulate membrane fluidity and permeability has been exploited to enhance drug delivery across biological barriers. Lipid-based drug delivery systems, such as liposomes and lipid nanoparticles, often incorporate cholesterol to improve stability and drug-loading capacity. By incorporating cholesterol into lipid bilayers, researchers can fine-tune membrane properties to control drug release kinetics and improve bioavailability. The presence of cholesterol also affects the interaction of drug carriers with cell membranes, promoting cellular uptake and intracellular drug delivery.

Furthermore, cholesterol plays a key role in the design of targeted drug delivery systems. Functionalizing cholesterol with targeting ligands allows specific delivery of drugs to diseased tissues or cells, minimizing off-target effects and enhancing therapeutic efficacy. Cholesterol-modified nanoparticles have been used to selectively deliver anticancer drugs to tumor cells by exploiting the overexpression of cholesterol receptors on cancer cell membranes. This targeted approach not only improves drug accumulation at desired sites but also reduces systemic toxicity.

Cholesterol in Drug Development

In addition to drug delivery applications, cholesterol derivatives have shown promise in drug development as scaffolds for the design of novel therapeutic agents. Chemical modification of the cholesterol backbone allows the synthesis of bioactive compounds with diverse pharmacological properties. For example, cholesterol-based prodrugs can be engineered to improve drug solubility, stability, and bioavailability. These prodrugs undergo enzymatic or chemical activation in the body to release the active drug, thereby enhancing the therapeutic effect.

Additionally, cholesterol analogs have been explored as potential drug candidates for a variety of diseases, including cardiovascular and neurological diseases. Structural similarities between cholesterol and steroid hormones have inspired the development of cholesterol molecules with hormone-like activity, opening new avenues for hormone replacement therapy and hormone-sensitive cancers. By exploiting the biological functions of cholesterol derivatives, researchers are expanding the range of drug targets and exploring innovative treatment modalities.

Case Study

The protein corona is a protein layer that forms on the surface of nanoparticles administered in the body, which largely affects the fate of the nanoparticles in the body. Although it is difficult to precisely control protein adsorption on nanoparticles, if the nanoparticles are modified with ligands with enhanced affinity for target tissue and cell homing proteins, the protein corona may be used to develop targeted drug delivery systems. Ahn et al. prepared a DNA tetrahedron with a trivalent cholesterol conjugate (Chol3-Td), which can induce enhanced interactions with lipoproteins in serum. It generates lipoprotein-associated protein corona in situ on DNA nanostructures, which is beneficial for targeting cells in the liver that express lipoprotein receptors in large numbers, such as hepatocytes in healthy mice and myofibroblasts in fibrotic mice.

Fig. 2. Cholesterol-mediated seeding of protein corona on DNA nanostructures (ACS Nano. 2022, 16(5): 7331-7343).

Chol3-Td was further used to deliver antisense oligonucleotides (ASO) targeting TGF-β1 mRNA to the liver for the treatment of mouse liver fibrosis models. The potency of ASO@Chol3-Td is comparable to that of ASO combined with the clinically approved liver-targeting ligand trivalent acetylgalactosamine (GalNAc3), demonstrating the potential of Chol3-Td as a targeted delivery system for oligonucleotide therapeutics. This study shows that controlling protein coronas on nanomaterials can provide a way to guide nanoparticles into targeted areas.

References

1. Nes, W.D. Biosynthesis of Cholesterol and Other Sterols. Chem Rev. 2011, 111(10): 6423-6451.
2. Ahn, D. et al. Cholesterol-Mediated Seeding of Protein Corona on DNA Nanostructures for Targeted Delivery of Oligonucleotide Therapeutics to Treat Liver Fibrosis. ACS Nano. 2022, 16(5): 7331-7343.