Liposomes

Question 1

What are liposomes

Answer 1

Vesicles that are made of lipid bilayer and capable of encapsulating drug

Question 2

What is the most common used phospholipid (hydrophilic hydrocarbon)

Answer 2

Phosphatidycholine
From soybean or egg yolk

Question 3

Why is cholesterol added to liposome structure

Answer 3

To stabilize the structure
Provides rigid vesicle
Prevents drug leakage

Question 4

How are Liposomes prepared

Answer 4

1- Preparation of film
2- Hydration of film
3- Downsizing of vesicle

Question 5

What happens in lipid film preparation
How are Organic solvents dried?
Shu mnaaml lal resultant lipid film

Answer 5

Lipids are mixed in organic solvents (chloroform or chloroform:methanol)
Organic solvents are heat labile, evaporated using dry nitrogen in fume hoot or using rotary evaporator
The result lipid film is completely dried by vacuum overnight and stored frozen until ready to hydrate

Question 6

2- Hydration of lipid, Shu bisir

Answer 6

Hydration is done by adding an aqueous medium
Then Agitation
To yield large multilamellar vesicles LMV
Having an onion like structure

Question 7

3- Downsizing, Shu bsta3ml
How do I get SUV? LUV?

Answer 7

Sonication: Sonic energy produces small unilamellar vesicles SUV

Extrusion: Lipid suspension is forced through polycarbonate filter to yield large unilamellar vesicles LUV

Question 8

Advantages of liposomes (4)

Answer 8

Improved pharmacokinetics and biodistribution of thereapeutic agents

Increase stability via encapsulation

They are non toxic, flexible, biocompatible, biodegradable

Can entrap both hydrophilic and lipophilic agents

Question 9

Disadvantages of liposomes (2)

Answer 9

Production is costly

They possess short half life (quickly detected by macrophage)

Question 10

Where are liposomes applied?

Answer 10

In pharmaceutical products and cosmetics

Used to improve bioavailability of large molecules
(interferon, gene delivery, cutaneous vaccines)

Question 11

Marketed Liposomes

Answer 11

Cancer agents
Fungal Disease
Analgesics
Photodynamic therapy
Viral vaccine

Check lecture for examples

Question 12

What is stealth liposome

Answer 12

Hinders detectio of liposomes by phagocytes
The polymers are attached to the system to improve safety and efficacy

Question 13

What is the Polymer used in Stealth liposomes

Answer 13

Polyethylene glycol (not detected by macrophages)

Process is called PEGylation

Question 14

How is PEG linked to liposome

Answer 14

By covalent linkage of liposome to PEG for protection of API from immune system thus decreasing immunogenicity

Question 15

How does PEG decrease Renal Clearance

Answer 15

By changes in the hydrodynamic size thus prolongs circulatory time
(PEG increases in size bl blood)

Question 16

Targeting liposomes
How do they act

Answer 16

PEg + a moiety that attaches easily to target cell
e.g. antibody to specific antigen tumor cell, upon attachment thus phagocytosis so it enters the cell
They migrate easily
e.g. Folic acid is added to surface since cancer cells aandon ktir folate receptors

Question 17

Types of liposomes

Answer 17

Small unilamellar (one lipid nilayer) 20nm
Large unilamellar <1micrometer
Multilamellar >1micrometer Onion shape
Multivascular
Ologolamellar
Giant Unilamellar aribe el 200micrometer