Question

You are designing different liposomes for drug delivery through the blood stream and for skin application as a topical lotion. Describe your selection of lipids for each application that would ensure the liposomes remain in a semi-fluid state between liquid-ordered and liquid-disordered states

Answer 1

Liposomes are small vesicle of lipid bilayer, mostly constructed artificially, for the several purposes like: drug dellivery. Different types of lipid molecules viz Cholesterol, phospholipids, sphingolipids etc are being used to build liposomes, depending on the purpose.

Now if we need to build a liposome that need to carry the drug through the blood and reach a particular target destination, we need to make a liposome that is with more stable lipid bilayer (or more in liquid ordered state), to prevent the drug's loss during circulation. Saturated phospholipids which contains longer acyl chains (viz. dipalmitoylphosphatidylcholine) can form a rigid bilayer. Though inserting cholesterol molecules within a less stable bilayer, formed by unstaurated (or polyunsaturated) lipids, can also introduce liquid-ordered structure. on contrary the insertion of cholesterols within a stable bilayer, with saturated lipids, can increase the disorderedness.

For liposomes that need to be applied on the skin or surface of the body, can be less stable as drugs need to be delivered just at the place of application. Thus utilizing unsturated lipids (better to be mixed with both cis and trans and also some amount of saturated lipids), easily avialable from several natural sources like phosphatidylcholine from eggs or bovine or soybeans. To increase the liquid ordered states, small amount of cholesterol can be inserted as per requirement.